Kim Skinner's Posts

Problems with NPIRC Pool Plaster Studies

Posted by Kim Skinner on January 28, 2010 at 11:10am

The National Plaster Council (NPC) began working with Cal Poly at San Luis Obispo in 2003 to study the causes of various plaster problems. The following information is a critique on the first two reports from professor Kachlakev (from Cal Poly) and the National Pool Industry Research Center (NPIRC), and contains information that they aren’t telling you.1. The primary conclusions or suggestions by Professor Kachlakev are as follows: Aggressive water and certain sanitizers are the primary cause of “etching deterioration,” craze cracking, and discolorations problems. (Phase 2, Pgs. 23, 39, 43, 45, 85) Our response: Aggressive water will cause etching of course, but it has nothing to do with deterioration of a defective (weak, soft, and porous) plaster surface, which can occur even with balanced water. Does the NPIRC have a scientific basis for using the term “deterioration” exclusively to describe an etching condition, and can they show that deterioration is never from other non-chemistry causes? On what basis do they suggest that salt chlorinators and trichlor sanitizers increase the amount or severity of craze cracking and discoloration on plaster surfaces? On what basis do they only “point the finger” at sanitizers or improper water chemistry for the cause of these plaster problems?2. In Phase 2, the professors stated that the “plastering application” for each test pool was performed identically. (Pgs. 32, 40, 44, 48, 85, 86) Since the test pools were troweled by different plastering companies and finishers with different training and experience, what evidence or proof backs up that claim? That unfounded claim is part of what enables the NPIRC to avoid addressing workmanship issues for discoloration, craze cracking, and deterioration of the plaster and conclude that imbalanced water chemistry was the only cause. What part of the project documented that different crews, with different backgrounds and experience levels generate zero variability in product quality?3. Low pH, low alkalinity and low calcium hardness were all included as parameters in the NPIRC investigations. All of these parameters are known causes of etching. However, high water:cement ratios, high calcium chloride content, premature filling, excessive late hard troweling… there are many workmanship factors that are also known to cause premature deterioration of a cement-based surface. It is highly questionable for the NPIRC to rule out variable workmanship issues as a possible and major player in early deterioration.4. Drs. Kachlakev and Pal co-wrote an independent report (given to the cement industry, but not to the pool industry) stating that their study (Phase 1, 2003-2004) did not control the fluctuations of water balancing properly, and did not monitor and record the readings in their test pools sufficiently to make specific, causative conclusions. To quote from the report, “While the observations from this study are useful in showing different stages and mechanisms of SA (spot alteration, or etching deterioration) in pools, they do not link SA to a specific set of construction practices or water chemistry conditions... (27th International Conf. on Cement Microscopy – Rothstein, Kachlakev, Pal, - April 2005) In other words, no conclusions on causes of deterioration should be made from their Phase 1 study. Yet Dr. Kachlakev, Pal, and other NPC members announced to the pool industry that the Phase 1 study “concluded” that water chemistry was the primary cause of etching deterioration. (Phase 1 June 2004 pg. 82, P&SN 9-3-04 & 1-17-04, IPSSAN Nov. 2006) Why did the professors make these two conflicting statements – one to their peers and a different one to the pool industry?5. Why did the NPIRC Phase 1 report dismiss variable water:cement ratios as relevant to the durability of plaster? (Pg. 22) It is a known fact that a high water:cement ratio on a cement surface negatively affects durability. (ACI Guide to Durability)6. The Phase 1 report indicated that too many plaster coupons were placed in water tanks that were too small – making it impossible to properly maintain water chemistry within targeted parameters (some tanks to be aggressive and some to be balanced), which resulted in water that fluctuated from very scale forming (pH readings higher than 9.0) to very aggressive (pH below 7.0 and TA below 60 ppm) in all water tanks. Yet, the NPIRC continued to compare and make conclusions based on these flawed results and insist that water chemistry is the major player in the deterioration of pool plaster. (Pg. 19) Why? Even though it is a fact that water chemistry can cause aggressive attack or etching of cementitious surfaces, the NPIRC did not adequately define “deterioration” nor did they show causation in this particular experiment.7. The Phase 1 report states that a high content of chlorine is “directly connected to discoloration of pool materials and could initiate etching deterioration.” (Pg. 36) There is no data in the report to support such a claim. On what basis do the professors make that statement?8. In Phase 1, the sections in the pools with 2% calcium chloride added (for fast hardening) were done first and allowed to harden for about 6 hours before submerging in water. In contrast, the sections without any calcium chloride added (which means they should have been allowed many more hours to harden before submerging in water) were done second, and not given any time to properly harden and hydrate before submerging in water. (Pg. 9) That plaster surface was far too soft and unhardened to be submerged in water, and it most likely suffered because of that fact. Certainly, when the inspection was done, the sections with calcium chloride looked and fared better than the other sections without any calcium chloride added. Anyone can see that was an unfair comparison. Yet the NPC and NPIRC announced that adding calcium chloride is a benefit and reduces “etching” of the surface. Of course, this contradicts ACI and PCA research and the conclusions by the RJ Lee Group and Construction Technologies Laboratories (CTL).In contrast to the NPC/NPIRC conclusions, and in agreement with RJ Lee and CTL, onBalance published a research report five years ago demonstrating that plaster (with and without calcium chloride) needs a few hours to properly harden before being submerged in water, otherwise the plaster surface gets dissolved and becomes very porous and leaches away (even by balanced water). That onBalance report was given to the NPC in 2004. No one with the NPIRC or NPC will address this obvious flawed protocol, and the conflict concerning the use of calcium chloride.9. In Phase 2 (2004-2005), calcium hardness readings in some pools occasionally fluctuated up and down 75 ppm to 150 ppm from week to week. That is not normal and very unlikely. The testing, according to the NPIRC report, was done using ASTM Standards (Pg. 15), which we now know is an untrue statement. It is obvious that the calcium readings were not being tested very accurately and were not being maintained within targeted parameters. In fact, between Phase 1 and Phase 2, it was not uncommon for some reported sets of readings (including pH and alkalinity) to be out of the targeted range over 50% of the time. How can conclusions be made when there were so many incorrect readings?10. Regarding the lack of accuracy, some test kit companies felt that when the NPIRC was comparing (and criticizing) the accuracy of test kits, certain appropriate procedures were not followed, or that there was a casual way with which the testing was done, which questions the accuracy of NPIRC’s own testing. In addition, Professor Kachlakev has stated that service techs cannot keep water in balance properly with once-a-week service visits. (IPSSAN November 2006) We disagree. Where is the data that proves this claim?11. We now know that ASTM Standards were not used by the NPIRC, but only a typical laboratory testing method. This was admitted by Dr. Kachlakev at the 2009 Western Pool and Spa Show, where he claimed that “ASTM” was merely a generic term for “lab method”. Obviously the American Society for Testing and Materials (ASTM International) would disagree with this assessment, and Dr. Kachlakev should know better. Should the NPIRC have made such a claim when it wasn’t actually using ASTM methods?12. In Phase 2, the actual readings show that Spa 13 had balanced or positive LSI water readings for the first four months. At the sixth week and fourth month inspection, this spa was reported to have “etching deterioration” and discoloration. Question: How does this spa prove that aggressive water caused these conditions?13. In Phase 2, the actual readings show that Pool 3 had balanced water, yet had discoloration at the sixth week mark and after eight months including craze cracking. Question: How does this prove that aggressive water caused these conditions?14. In Phase 2, the actual readings show that Pool 4 had balanced water, yet was reported to be one of the worst “etching deterioration” pools after eight months. Question: How does this prove that aggressive water caused that condition?15. In Phase 2, the actual readings show that Pool 12 had balanced water, yet after eight months was reported to have heavy discoloration, a significant amount of craze cracking, and etching deterioration. The NPIRC report implies that imbalanced water or certain sanitizers cause these conditions. Question: Where is the proof to support these claims?16. In Phase 2, the report stated that Pool 7 was one of the best looking pools overall. Yet, the readings indicated that this pool had a slightly aggressive startup procedure, and that slightly aggressive water existed occasionally over the eight month period. Question: Why did Pool 7, which had more aggressive water, look and fare better than Pool 3, Pool 4, and Pool 12, which had more balanced water than Pool 7?17. In Phase 2, only three of the twelve test pools had recorded chlorine readings for the entire eight month test period. The other nine pools have no recorded chlorine readings for the final six months of their test period. Why aren’t there chlorine readings after two months? Is this acceptable research? Does it prove that chlorine is involved in discoloration?18. In Phase 2, Pool 3 was not to have any cyanuric acid added, which was to be compared to Pool 9 that would have 50 ppm of cyanuric acid added. But according to the data, Pool 3 had 50 ppm of cyanuric acid added just like Pool 9, and the researchers still made comparisons and conclusions – specifically that cyanuric acid is not a player in discoloration or deterioration. This, in turn, contradicts the NPC start-up procedure publication, which claims that cyanuric acid does cause plaster degradation… What happened?19. In Phase 2, Pool 1 was a “salt” pool and had salt added after 30 days, which increased the salt level to 3200 ppm. But data for that pool shows that the Total Dissolved Solids level (TDS, which of course includes salt) never increased beyond 800 ppm, which seems to indicate that either the TDS readings were made up or that the salt was never added. What happened?20. The Phase 2 protocol specified complete chemical testing of all twelve test pools and two spas every day for two months, then two or three times per week for the remaining six months, and once a week with ASTM techniques. (Pg. 15) Yet, according to the data provided, the testing wasn’t performed as claimed. At times, no testing was performed for 9 to 13 days at a time. Why?21. For Phase 2, the testing of the carbon dioxide content was performed by titration. A review of the data and using the nomographic method for comparison indicates that the carbon dioxide amounts tested and recorded were often significantly incorrect. Shouldn’t the NPIRC know that water with cyanuric acid and boric acid present interferes with the results? We have specifically called this testing incompatibility to the attention of the NPIRC committee’s “Technical Advisor” Greg Garrett almost two decades ago. Why was this testing by the NPIRC so inaccurate? Why did neither the NPIRC’s staff chemist nor the “technical director” catch the problem?22. In Phase 2, the NPIRC reported that the “Acid” and “pH neutral” startup procedures proved superior and prevented “etching deterioration” when compared to the traditional startup method, which reportedly resulted in significant etching deterioration. (Pgs. 29, 44, 86) How is it possible that a “Traditional” (balanced) water startup resulted in etching? How is it possible that an “Acid” (a.k.a. Zero Alkalinity) startup procedure did not etch a new “non-hardened or cured” plaster surface? Should not this counter-intuitive result be addressed and explored?23. In the Phase 2 report, it is suggested that craze cracking, discoloration, and deterioration of the plaster was only related to water chemistry imbalance and certain sanitizers. (Pgs. 23, 39, 43, 45, 85) Yet, it has been documented by the ACI and PCA that improper workmanship and practices (not water chemistry) will lead to increased craze cracking and discoloration. Why did the NPIRC rule out possible workmanship issues and only point to water chemistry and sanitizers as leading to these plaster problems? Do they have unrevealed information that throws the American Concrete Institute and the Portland Cement Association data in doubt?24. It has been well documented (in the cement and concrete industry) that calcium chloride additions over 2% of the weight of cement is considered detrimental to the durability of a cementitious product, will increase shrinkage and craze cracking, and will also discolor (darken) the cement. Why did the professors state that a “moderate amount of calcium chloride (up to 3.5 %) is beneficial to a cement product?” (Pgs. 63, 66, 68)25. The NPRIC Phase 1 report mentions that the leaching of calcium hydroxide is what initiates the development of “etching deterioration” and can only be dissolved or etched away by aggressive water. (Pgs. 31, 35, 36, 38) That is not true, and the professors should know that calcium hydroxide can be dissolved by what the pool industry considers balanced water, particularly from a porous surface. Water balance predicts over- and under-saturation relative to calcium carbonate… a much more insoluble material than calcium hydroxide.26. Finally, the NPIRC and NPC are promoting the use of more durable plaster products to sell to pool owners. Their reasoning is that typical white plaster is inherently weak, and that that “imperfect” water chemistry and maintenance programs (which the NPIRC says are inevitable) will quickly deteriorate this “naturally” weak product. Their “solution” is to insist on selling quartz and pebble finishes to customers, which will supposedly eliminate the problems that result with standard white plaster. Isn’t it interesting that there are no specific suggestions (from the NPIRC) on the need for proper workmanship issues to improve durability? This agenda removes incentive for plasterers to perform quality work if they are allowed to blame all investigated plaster defects (discoloration, cracking, and deterioration) on water chemistry maintenance. Obviously, plasterers will benefit by being paid to redo the pool again (much sooner than usual) and with the more costly upgrade. Yet, not surprisingly, the NPC has stated that if problems do develop on their more costly material upgrade, it is most likely caused by improper water chemistry too!Although not exhaustive and complete, we feel that this list can be a good starting point toward assessing what we can and cannot yet conclude from the Cal Poly research, and what kinds of things need to change in order to make it the learning facility it could be.

Calcium Nodules in Pools

Posted by Kim Skinner on January 15, 2010 at 12:30pm

Calcium Nodules in PoolsWhat are calcium nodules? In swimming pools and spas, they are small mounds, or “slag” piles of calcium carbonate which are formed from material that has been released from the plaster. Here are some pictures of calcium nodules:

In the cement/concrete industry, this phenomenon would be called a form of “efflorescence” (but in keeping with the spirit of common pool industry practice, we call them “calcium nodules” instead…)The most common type of nodule is the “delamination” nodule. These nodules grow because of a void (usually a bond separation) between plaster and its substrate. Here is the sequence:

Under normal conditions, the plaster (white) is exposed to the water (blue), is bonded to the gunite substrate (speckled), which in turn rests on dirt (tan). (Picture not to scale…)When the plaster is new, and the pool is first filled with water, calcium hydroxide bleed-off from the plaster surface dilutes into the pool water (blue) and is converted to non–soluble calcium carbonate (plaster dust).Continuous “rinsing” of the hydroxide bleed-off by the circulating pool water, as well as normal pool maintenance (such as brushing), prevents a buildup of hardened plaster dust on the new plaster surface.

Sometimes, an air cavity (a bond failure) can form between the gunite and the plaster, or between multiple layers of plaster. This is referred to as “delamination” and the cavity is referred to as a “void.” As long as the void is not connected to the surface of the plaster, the fact that the void even exists may not be known. Unless the plaster completely breaks free from the surrounding plaster, creating what is referred to as a “pop–off,” or unless the delamination is extensive, this is not considered by the plaster industry to be a defect.

In some cases, however, the void is connected to the surface by a small pinhole or hairline crack. Pinholes and cracks are often created from structural flexing of the delaminated plaster.

Gradually, water from the pool penetrates the void via the hole or crack, and creates a localized chemistry environment completely separate from the water balance in the pool. As calcium hydroxide bleeds into the void water, it creates a calcium–rich, high pH solution like a little “calcium/pH factory” beneath the plaster surface. The pinhole or crack is not of sufficient size to create a rinsing effect like that which occurs at a new plaster surface.

Calcium–rich void water and pool water containing bicarbonate alkalinity, in contact with each other at the plaster surface, react with each other, which results in the production of an insoluble calcium carbonate by-product.

If the conditions are right, this insoluble calcium carbonate can build up a “slag pile” around the exit point, thus forming a nodule.Attempts to remove a nodule through scraping or sanding can be successful – but the node may reform on the same site once or twice, until all of the source hydroxide is used up. Then it shouldn’t come back.Acid washing nodules off usually isn’t the best response, since the calcium carbonate it is made of is the same stuff much of the plaster is made of. So to dissolve the one, you also dissolve some of the other.Plugging the hole, by drilling and epoxying, has been successfully used to stop nodule formation, since water can then no longer travel in either direction. But remember, draining the pool may cause more delaminations to occur, so this repair should be performed under water.It is important to keep in mind that nodules are a symptom, rather than the disease itself. The disease is bond failure, cracking or some other imperfection that allows water “to boldly go where no water has gone before” (sorry, Captain Kirk).Nodules that form on horizontal surfaces like pool floors end up round shaped:While those that form on walls drip downward, reminiscent of some stalactites:Although the calcium carbonate is white, and thus pure calcium nodules are white, when the crystalline matrix incorporates or absorbs dirt, metals, or other contaminants the nodule takes on a color:Another type of nodule is associated with crazing (small cracks in the plaster) rather than with delamination. Craze cracking can form from high heat, excessive wind, low humidity, or from shrinkage due to excess water or calcium chloride in the mix. Plaster is capable, to a certain degree, of “backfilling” craze cracks with calcium hydroxide, which later carbonates. (Technical term: autogenous healing)Some of the hydroxide releases into the pool water, and is converted to calcium carbonate “plaster dust.” However, if conditions are right, especially if an extensive network of shrinkage micro fissures is present, nodules can form at these initiation sitesIf the surface is sanded or acid washed, the existing nodules may be removed. However, more of the craze network is exposed, and many more nodules may then be formed.

Nodules can even grow on tile grout! This is actually two nodes – a large one to the upper left and a smaller one to the lower right. Notice the “volcano hole” where the continuing process happens!But the mechanism is the same. In this instance, the source of the calcium- and hydroxide-rich solution is a delamination in the grout/plaster/gunite interfaces:Nodules can also form on fiberglass surfaces! However, research has shown that in these instances, pinholes existed in the fiberglass, and the source of the node material (calcium) was the plaster/gunite beneath the fiberglass coating:For decades, it was understood among plasterers that calcium nodules primarily formed due to bonding failure (delamination) of a new coat of plaster, and occasionally from severe craze cracking, and that they were responsible for this plaster defect. Plasterers learned that bonding failure rarely occurs on fresh gunite substrates (new pools); however, bonding new plaster (replaster) to old plaster surfaces can occasionally be difficult to achieve. This is why most calcium nodules occur in replaster jobs.Unfortunately today, some in our industry (primarily plasterers) will claim that faulty water chemistry maintenance is the direct cause of nodules. The National Plaster Council’s 2009 Tech manual also suggests that improper water chemistry maintenance causes calcium nodules to form on cracks in the plaster surface. That is absolutely incorrect. Service techs should not accept the blame that their chemical treatment caused this plaster defect. Aggressive water would actually prevent nodules from forming, and properly balanced water will not prevent nodules from forming, and actually facilitates the visible growth that exposes the underlying problem.

Bicarb StartUps #2

Posted by Kim Skinner on September 28, 2009 at 1:32pm

The onBalance Bicarb Start Up method is as follows, including pictures.Step 1 – Pre-testing the Water• We Test the chemistry of the tap water that will be used to fill the pool. The key characteristics we observe are pH, Alkalinity, Hardness, Copper and Iron.Step 2 – Calculating the Chemical Dose• We Add the Alkalinity and the Hardness numbers together. Then we subtract that number from 500. The result is the amount of sodium bicarbonate in ppm to add. For example, if the fill water Alkalinity is 90 and the fill water Hardness is 200, then 210 ppm of new bicarbonate needs to be added: 500 – (90 + 200) = 210• Then we apply the Simplified Dosage Formula for raising alkalinity using sodium bicarbonate: (Volume ÷ 71,400) x ppm to increase = pounds to add• For example, if the pool will hold 20,000 gallons, and we want to add 210 ppm of bicarbonate alkalinity: (20,000 ÷ 71,400) x 210 = 58.8, or about 60 pounds to add• If the total alkalinity and calcium hardness combined amount is 500 ppm or higher, then no addition of sodium bicarbonate is necessary.Step 3 – Setting up the Delivery System• We then set up a 55 gallon plastic drum that has garden hose connections added to it. The drums include the following modifications:– An 8 to 10 inch hole is cut in the top of the barrel to facilitate pouring in the bicarb– A female hose connector is mounted halfway up the “back” or “deck” side of the barrel– Three male hose connectors are mounted about 4" below the top lip on the “pool” side of the barrel, enough to make sure that sufficient output hoses are provided to handle the pressurized input from the tap without overflowing the drum– One fitting is mounted at the bottom of the pool side of the barrel, which leads to a plastic ball valve and then a male hose connector• To start the process, a hose is run from the home water source to the deck-side fitting, and three hoses are run from the top pool-side fittings to the bottom of the pool, with the ends wrapped in cloth and taped. Bicarb (we use technical grade sodium bicarbonate) is added to the drum before any water is turned on.• After adding the bicarb, the pool is ready for filling. The water is turned on, fills the barrel, and gravity-flows out the three hoses into the pool. The powder will slowly dissolve as the pool fills. When the pool is full, the barrel is drained through the bottom pool-side drain fitting into the pool, and any remaining powder is rinsed into the pool.Step 4 – pH Adjustment• If the pH of the fill (tap) water is over 8.2, we add 1 quart of acid to the drum once the drum is full of water.

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Step 4 – pH Adjustment• If the pH of the fill (tap) water is over 8.2, we add 1 quart of acid to the drum once the drum is full of water.Step 5 – Determining Fill Delay, Turning On the Water• In consultation with the plasterer, we decide when the water will be turned on relative to the crew finishing the pool. We encourage the plasterer to allow at least 6 hours between final troweling and turning on the water.• At the pre-determined time, we ensure that the water is turned on and that the flow through the barrel to the pool is working properly, without leaks.• Working with the homeowner, we ensure that the water fills uninterrupted from main drain to surface tile.Step 6 – Making Adjustments• Once the pool is filled, we double check the pH, which should be right at 8.3. This requires the use of a pH meter, since 8.3 is at the extreme high detection range of phenol red.• We double check the Alkalinity, which should be anywhere from 100 to 350 ppm.• If the pH is 8.2 or higher, we add acid to adjust the pH down to the high 7 range – 7.7 to 7.9ish.• If the Hardness level is below 150 ppm, we add calcium chloride as needed, using the Simplified Dosage Formula for adding Hardness (see below). Be sure the pH is below 8.2 before adding calcium chloride.• We recheck the copper and iron levels and add chelating agents as needed.• We then add cyanuric acid, chlorine, etc. to reach to our target maintenance levels.Step 7 – Monitoring the Progress• Over the course of the next two weeks, we ensure that the pool is being brushed and filtered per the plasterers’ specifications, and chemically maintained per our standards.• For the first month after fill, we allow the alkalinity to remain as high as it was from the start-up, and ensure that the pH remains at 8.2 or lower.Step 8 – Final Balancing• After a month, we begin adding acid until the Alkalinity reaches the target range.• We aren’t in any great hurry to finish that – as long as the pH remains below 8.3, there will be no plaster dust and no scale formation.P.S. For the first month of the bicarb program, it is better to use dichlor for sanitizing instead of liquid bleach or cal hypo due to the high pH effects of these products.Simplified FormulasRaising TA with Sodium Bicarbonate: (Volume ÷ 71,400) x ___ ppm desired change = ___ poundsRaising Hardness with Calcium Chloride: (Volume ÷ 83,000) x ___ ppm desired increase = ___ pounds(Amount in pounds to increase calcium hardness with 77% calcium chloride strength – use 101,700 as divisor for 94% strength)An Interesting Example:This pool/spa combo, featuring black plaster, was set up to be bicarb-started. You can see the barrel and hoses in the background. When we came back that evening, the pool was crystal clear, but the spa looked like it was full of milk (especially once we brushed it!). The homeowner had come home and decided to fill the spa using non-bicarbonate tap water. What a difference!

Of course, most would assume that scale would develop because of the high alkalinity level (having a positive LSI). But if the bicarb program is done correctly, scale doesn’t form.The important issue is that new plaster surfaces are soft and not completely hardened and the calcium hydroxide on the plaster surface is somewhat soluble and can be dissolved away by typical balanced water. However, if enough bicarbonate is present or is added to the tap water, the plaster surface, once filled, becomes carbonated within the first month, and a denser, less soluble, and harder surface is the result.onBalance is a consulting group consisting of Kim Skinner, Que Hales, and Doug Latta

Bicarb Startups #1 of 2

Posted by Kim Skinner on September 23, 2009 at 4:59pm

In a nutshell, the “Bicarb Start-up” is a method which helps eliminate the formation of “plaster dust” in new plaster pools and which results in denser, smoother, more durable plaster than other techniques.When a new plaster pool is filled with typical tap water, it is normal for a small percentage of cement paste at the surface to dissolve into the water, and form a solid calcium carbonate precipitate – which we in the pool industry call “plaster dust.” This plaster dust is then brushed and filtered and brushed and filtered and so on, until it is gone.In a traditionally started pool, with a pH around 7.4 to 8.0 and a TA of about 100 ppm, the form of calcium that “bleeds off” into the water from the plaster surface is calcium hydroxide, which has such a high pH (in the 10+ range) that under normal filling procedures (i.e., when the water is not pre-treated), the pH of the pool water jumps immediately and almost always exceeds 8.3 and sometimes as high as 11.0 – which begins to convert the calcium hydroxide in the water into scale. This is the “plaster dust” that we see for the first 3 weeks.The bicarb start-up method begins by adding bicarb (sodium bicarbonate) to the fill water before it enters the pool. This type of fill water helps “fix” or convert “in place” most of the calcium hydroxide in the surface by converting it to the more durable calcium carbonate. As a result, less calcium is released into the water, and the surface retains more of its original constituents resulting in a denser finish.Now, to understand start-up chemistry, there is a pH value to keep in mind – pH 8.3. Above 8.3, calcium carbonate, or scale is likely to form, and the higher the pH rises above 8.3, the more carbonate scale is formed. So we call high pH levels (over 8.3) “scaling” pH levels. Below pH 8.3, calcium tends to stay in a soluble “bicarbonate” form.Saturating fill water with baking soda not only helps keep the pH at 8.3 or below, but it also provides enough bicarbonate to impede and reduce the dissolution of calcium hydroxide from the plaster surface. It does this by reacting with and converting calcium hydroxide on the plaster surface into a protective layer of durable calcium carbonate, thereby creating a denser and harder surface.The primary, immediate difference noticed when doing a bicarb start instead of a traditional start is that there is virtually no plaster dust. Over the long term, there is also better, more durable and smoother plaster.While the acid start will also eliminate plaster dust, help colored plaster pools to retain their color, and dissolve white deposits; it also has a serious drawback to its method. Acid start-ups, where a minimum of four gallons of acid is added soon after the pool is filled with water, will usually dissolve all plaster dust formed, but unfortunately also dissolves and uniformly etches (as determined by magnification) the entire plaster surface at the same time. This process leaves the surface rougher and porous (as seen under magnification), which in turn makes it less durable, easier to stain, and harder to clean in the long run.Furthermore, once the acid start program is over, it can be tricky to raise the pH and alkalinity and balance the water without creating scale. In addition, it is often the case that the person who performs the acid start realizes the short-term benefit (a clear non-scaled pool), but the person who provides the subsequent maintenance suffers the long-term deficit (rougher plaster and worse staining).We know of several pool plasterers who had difficulties creating and maintaining consistent color on colored plaster, quartz aggregate pools and with hydrazzo pools. These plasterers were using the acid start-up method trying to stop white scale from developing on these special pools.When these plastering companies began Bicarb starting all of their colored cement pools, the color was darker and more consistent, and the white film deposits no longer formed! In addition, over time, these bicarb started pools retained their superior finish much longer due to the smoothness and the additional density of the protective, carbonated surface. Years later, the process of removing dirt and other stains by acid washing is vastly improved.The Bicarb start-up is always the best start-up method to use on plaster pools. However, it is also important to have quality and durable pool plaster to start with. Improper plastering practices can reduce the effectiveness of a bicarb start-up and all other start-ups methods or programs.If plaster has too much water in the mix, too much calcium chloride added, and too much water added while troweling, and is filled with water too soon after completion, it will result in a less durable and lower quality plaster finish. The above improper cement practices create greater porosity and more soluble plaster components which results in more plaster dust forming on the plaster surface during the first few weeks.A greater porosity can only result in a surface that is more susceptible to dirt and mineral staining months later. Acid washing will be less effective in removing stains and more likely to cause more “wear and tear” to the plaster surface.But as mentioned before, a bicarb start-up will always help in creating a denser, smoother, and more durable plaster surface despite these other factors.Next, part 2. The step by step process.

Pool Startup Chemistry for Plaster

Posted by Kim Skinner on September 14, 2009 at 9:53am

Four years ago, the National Pool Industry Research Center (NPIRC) at Cal Poly reported that they had studied the effects of three different chemical startup procedures on pool plaster. (Phase 2, October 2005). The three chemical startup procedures were;• the “Acid” startup – where enough acid was added to lower the pH to 4.5 and alkalinity to zero for three days• the “pH-Neutral” startup – where one gallon of acid was added to an 8000 gallon pool, then balanced after 3 days• and the “Traditional” startup where the water was maintained in a slightly alkaline (basic) water conditionIn published results the NPIRC claimed (after waiting eight months and using just visual observations) that the Acid and the pH Neutral startups proved superior and provided plaster with better protection against etching deterioration when compared to the Traditional startup, which was reported as resulting in significant “etching deterioration.” This begs the question: How does a balanced water startup technique such as the Traditional startup result in etching deterioration? And yet the acid startup had no etching?Is the NPIRC study accurate regarding the effects of the three different startup procedures? What really is the best way to chemically start up a new plaster pool?All three of these startup techniques were recently studied by onBalance, which also included a fourth technique known as the Bicarb startup (which involves water pre-treatment with sodium bicarbonate).Two different analyzing methods were used to determine which chemical startup provided the best effect and protection for a new plaster surface. One method was microscopy (40X Magnification) to visually examine the plaster surface. The other analysis was performed by determining the calcium increase of the water that the plaster coupons were submerged in.Well made, high quality plaster coupons were formed and placed in water after 24 hours of drying in moderate temperatures. Several coupons were each (separately) placed in water where conditions duplicated the “Bicarb” startup. The second set of coupons were placed in typical balanced water (simulating a “Traditional” startup), the third set were placed in moderately aggressive water (an LSI of –0.8, similar to the so-called “pH Neutral” startup), and the fourth set were placed in water that simulated an “Acid” startup (which equals a very aggressive –4.0 LSI). After three days, the coupons were removed and the calcium level in each water tank was tested. The Bicarb startup water had a zero to 2 ppm increase in calcium, the Traditional start water had an average calcium increase of 7 to 10 ppm, the pH Neutral (moderately aggressive) startup water had a 15 to 20 ppm calcium average increase, and the Acid (or zero alkalinity) startup process had an average calcium increase of 60 to 80 ppm. An increase in calcium (in the water) indicates a loss of calcium from the plaster, and a resultant increased porosity of the surface. This produces a weaker surface which can lead to eventual staining. These results indicated that the bicarb startup program had the least amount of calcium loss, preserving the high surface density which provides the best protection for the plaster surface.While all coupon samples were white and smooth to the touch, when 40X magnification was used to examine the plaster surface, we found that the Acid startup coupons were slightly etched, with the thin layer of cream (cement) missing, the aggregate exposed. On the other hand, the Bicarb startup coupons were very smooth, with the cement cream layer still intact and the aggregate not exposed. The other two methods fell in between the Acid and Bicarb results, with the Traditional startup coupons showing just a slight effect, and the pH Neutral startup coupons just a little more exposed aggregate than the Traditional. This microscopic examination was consistent with, and confirmed the results found by using the “calcium increase” analysis method. But understand, this observation is with a microscope; the unaided human eye cannot see the difference, and the hand cannot feel the difference.The results obtained by the onBalance study differ greatly from the results obtained by the NPIRC, and in fact, are completely opposite. It would appear that the NPIRC did not consider differences in workmanship and other variables as possible causes for the deterioration and discoloration.It is evident that the Acid startup is the most detrimental method and causes irreparable harm to a new plaster surface. While the Acid startup may dissolve plaster dust and help the surface look good for a few months, this more coarse and porous plaster surface will likely deteriorate and stain earlier and easier. The Bicarb method, on the other hand, is an improvement on the industry standard Traditional method.onBalance is a consulting group comprised of Que Hales, Doug Latta and Kim Skinner

Aggressive Water VS Poorly Made Plaster

Posted by Kim Skinner on August 27, 2009 at 4:19pm

How aggressive does water need to be and how long does it take to visibly etch well-made plaster? And if plaster is not well-made, what can even balanced pool water do in terms of early deterioration and discoloration? The following are results of our study.“Good” Plaster, “Bad” Water - The first part of our study was designed to determine the amount of calcium that can be dissolved or etched away from well-made pool plaster by aggressive water. Several plaster coupons were made with a proper (low) water-to-cement ratio, with no calcium chloride (an accelerator), and were allowed to cure and harden for 24 hours before being individually submerged in aggressive water for six months. The beginning calcium level of the water they were placed in was 80 ppm, and the water was maintained continually with a Langelier Saturation Index (LSI) ranging from -0.6 to -1.1. After six months, the measurement of the calcium in the water tanks showed an average increase of 50 ppm. (Note: An increase in the amount of calcium in the water indicates a loss of calcium from the plaster surface). No discoloration of these coupons was visible, the coupons remained very white and smooth, and there was no visible shrinkage or craze cracking.“Bad” Plaster, “Good” Water – The next part studied how much calcium can deteriorate, or can be removed from poorly made plaster that has been maintained in balanced water. The beginning calcium hardness level was 180 ppm and was maintained in a continual LSI range of +0.2 to +0.5. The “poorly made” plaster coupons were made with a high water-to-cement ratio, a high amount of calcium chloride, and they were placed in water only one hour after final troweling, representing three common improper plastering practices. Only two days later, the calcium level of the water in the tanks was tested, and the result was an average increase of 160 ppm! Since the ratio of plaster surface area of the coupons to gallons of submersion water was similar to that of an actual pool, we can calculate that this amount of calcium loss from a plaster surface is equal to about 26 pounds of calcium carbonate from a 20,000 gallon pool. Some gray discoloration and minor craze cracking of the coupons was also observed, which confirmed the already known effects of using excessive amounts of calcium chloride and a high water-to-cement ratio.As can be seen in this study comparison, three times more calcium was quickly lost from the plaster surface due to the improper plastering methods than is lost from significantly aggressive water attacking well-made plaster for six months. A loss of calcium from the immediate surface increases porosity which directly affects the aesthetic durability of a pool plaster surface. Simply put, it reduces plaster’s ability to hold up well in a water environment and makes it more susceptible to staining or discoloration.There are data from other sources that support the results of our study. The ACI and (PCA) have documented the negative and detrimental effects from using high water-to-cement ratios, and high calcium chloride contents.Also, an objective review of the data from the NPIRC at Cal Poly reveals some similarities to our results. For example, in their Phase 1 protocol, the plaster sections that were submerged in water immediately after final troweling looked visibly worse in comparison to plaster sections that had six hours of drying time before being submerged in water. In Phase 2, many of the test pools were reported to have had either visible deterioration or discoloration in just six weeks time even though they were in balanced (non-aggressive) water. These results indicate something other than aggressive water chemistry as the cause of the deterioration and discoloration of the NPIRC test pools, although this information was not included in their final conclusions.Another known improper plastering practice which correlates to the effects of a high water/cement ratio, is the act of adding water to a plaster surface while troweling. Doing this increases the water–to-cement ratio where the water is added and troweled into the surface. This procedure is known to cause increased laitance, increased porosity, weakness, softness, shrinkage (craze cracking), discoloration, and a less-durable finish. That is why both the ACI and the PCA advise against adding water while troweling a cement or concrete surface, which would include pool plaster. This improper practice simply adds to the negative effect mentioned above.It should not always be assumed that an increase in calcium (from the tap water readings) had to be the result of aggressive water dissolving calcium from the new pool plaster surface, but instead may be the result of improper workmanship practices. Additionally, any discoloration of plaster, whether white plaster with dark blotches or gray streaks, or dark colored plaster with white streaks, should not automatically be blamed on aggressive water. If the pool water has been maintained properly and reasonably well, and within APSP standards, a review with the plasterer regarding the quality and workmanship of their product is appropriate. Fortunately, today’s technology provides the ability to analyze pool plaster for its water-to-cement ratio, the content of calcium chloride, and whether etching has occurred due to aggressive water or whether the plaster has simply deteriorated and discolored due to improper plastering practices.onBalance is a consulting group comprised of Que Hales, Doug Latta and Kim Skinner

Making Durable Pool Plaster #2 of 2

Posted by Kim Skinner on August 18, 2009 at 12:35pm

For one through seven, see "Making Durable Pool Plaster #1"Eighth, once the pool has been plastered and is finished, the filling of the pool with water should not be started too early. Conditions vary, but as a general rule the water should not be turned on for at least 6 hours after finish troweling. This allows the plaster to properly harden before being submerged in water. Even balanced tap water can dissolve certain plaster components from an insufficiently hardened plaster surface, creating increased porosity and early deterioration. onBalance conducted a research study that documented this fact.Ninth, steps should be taken to ensure that the fill water is appropriate for filling a new plaster pool. Studies have shown that 75% of the damage done by aggressive water to new plaster surfaces occurs within the first 24 hours, although this deterioration is uniform. Other new plaster surface discolorations such as drips, splotches, spotting, trowel marks, hand and footmarks, etc. are caused by finishing errors. Surfaces can be further damaged by using aggressive (acid) start-up techniques, which can increase the amount of uniform surface loss. Baking soda startups, for example, will both neutralize aggressive fill water and also promote a superior plaster surface.Tenth, once a pool is filled, balance the water and keep it that way. Although this does not “create” long lasting, durable plaster as the above practices do, balanced water chemistry helps preserve that surface. Long experience has shown that aggressive water uniformly etches plaster, and over-saturated water scales it. The Saturation Index is a good guide – water should have a saturation index value in the range of –0.3 to +0.5. This range does not actively promote either scaling or etching.White plaster is a good and relatively inexpensive surface that many pool owners desire. Although pozzolans, blended cements, quartz and pebble aggregates, can provide even better results, they do not negate the need for proper workmanship, and the last century has shown that most standard white plaster lasts about 20 years with reasonably good maintenance. It is not inherently weak, and unable to stand up to the “real world” pool environment, including the vagaries of chemistry and maintenance. This is evidence that many pools are plastered correctly by good plasterers.Now, in the real world we all realize that some variables will be outside the control of even the most professional tradesman. Weather happens, materials that are assumed constant may vary, good-intentioned but unknowledgeable outsiders intervene, etc. We also understand that pool plaster is a hand-crafted product, and nothing in nature – especially where humans are involved – is perfect.However, a plaster finish can also be made poorly. If only one minor abuse of the above guidelines is performed, then it probably won’t manifest itself with any visible adverse effect early on. If more than one of the above mentioned practices is significantly abused, then a far quicker deterioration can take place even in balanced water. The greater amount of “plaster dust” a new plaster pool creates is an indication that some improper practices occurred. Virtually no plaster dust in new plaster pools would occur if all of the above proper practices and workmanship issues were followed correctly.Unfortunately, during the early stages of the plaster’s age, many problems that have commonly been attributed to improper water chemistry may actually be due to one or more of the above workmanship issues.As a result of our investigations, when plaster begins to show signs of discoloration or deterioration within a few months, and the water balance has been maintained in a reasonably balanced range, we suggest that those involved should investigate whether the above guidelines for providing and making quality and durable plaster were followed. Today’s technology provides the ability to analyze plaster for most of the above-mentioned issues, such as water/cement ratios, cement/aggregate ratios, calcium chloride contents, whether the surface is more porous than the interior matrix due to water additions, and whether the plaster has been etched by aggressive water or has simply deteriorated due to being of poor quality.Adhering to good plastering practices, standards, and workmanship, and then following accepted water balance practices will eliminate most all pool plaster problems, pool owners will be happy, and our industry will prosper.Provided by onBalance, a consulting group comprised of Que Hales, Doug Latta and Kim Skinner

Making Durable Pool Plaster - Lessons Learned #1 of 2

Posted by Kim Skinner on August 12, 2009 at 11:00am

Our field and lab research, coupled with consulting and analysis services from two of the best cement failure-analysis labs in the country, has led to newer and better explanations for the causes and mechanisms of many plaster failures, including etching, scaling, nodules, delaminations, spotting, streaking, staining, discolorations, and general surface deteriorations. Together with the professional labs, we have been able to demonstrate that known concrete/cement science applies to pool plaster.Here is what we would offer as a sort of “Ten-point checklist” of issues leading to either good or bad pool plaster.First, the best cement/aggregate ratio is about 1 part cement to 1.5 – 1.75 parts aggregate (marble sand or limestone). For quartz finishes, the mix is a little richer. This produces a higher quality pool plaster product than either richer (more cement) or leaner (more sand) mixes. Plaster that is too rich tends to shrink and crack, and plaster that is too lean is unworkable and isn’t durable. The cement and aggregate should also be selected with care – it needs to be of good quality, consistent, and of an appropriate grade for use in pool plaster. (This also applies to any admixtures).Second, a water/cement ratio of .50 or less is best when mixing plaster. The American Concrete Institute (ACI) and the Portland Cement Association (PCA) have both established that lower water/cement ratios (less than .50) provide for better quality cement which can resist occasional exposure to mild acids. Lower water/cement ratios increase density and reduce permeability, porosity, shrinkage (craze cracking), and movement of water within the cement product. Higher water/cement ratios can result in a finished product that does not have adequate protection or long-term durability against the natural effects of water and the environment.Third, plaster should contain as little calcium chloride set-accelerant as possible, and never more than 2% to the amount of white cement. (Colored plaster, of course, should not contain any calcium chloride.) It has been documented by the PCA and other cement laboratories that using more than this amount increases discoloration, mottling, and shrinkage of cement. Alternatives to calcium chloride, which do not have these downside effects, are available.Fourth, a plaster mix should be mixed thoroughly, but also not too long. It is recommended that if the plaster has been mixed for more than 90 minutes, the plaster mix should be discarded.Fifth, water should not be added to plaster surfaces while troweling because of the strong risk potential. It has been documented by the ACI and PCA that doing so (“skewing the surface water-to-cement ratio”) increases porosity, shrinkage (cracking), streaking, spotting, and variable discoloration. Small amounts of water for trowel lubrication doesn’t necessarily seem to have a significant adverse effect on the plaster surface – most visible problems require a combination of water finishing, chloride abuse, and other improper practices, and take time to become exposed. But it is very important not to “work” or force additional water into the plaster surface while troweling. This particular practice can weaken the surface and show deterioration and discoloration (or color variation) much sooner than usual. Dark colored plaster is even more susceptible to discolorations from water additions than white plaster.Sixth, well-timed hard troweling can help produce a good dense plaster finish. However, if the plaster surface has overly hardened before a smooth surface is obtained, then late hard troweling can cause discoloration and color variation, especially when calcium chloride and extra water is also used. This also has been documented by the PCA.Seventh, plastering in extreme weather conditions can lead to durability problems. The ACI and PCA both mention that placing cement-based products on days or in conditions that are either too cold or too hot adversely affects the quality and durability. However, these problems can be avoided by “tenting” the pool, thus protecting the plaster surface (and the plastering finishers!) from the extreme temperatures. For example, tenting a pool in extreme high temperatures, and perhaps even directing air from an evaporative cooler under the tent, can help the plaster to retain its moisture and thereby properly cure and harden.

The State-of-the-Art Pool Service

Posted by Kim Skinner on July 29, 2009 at 8:19pm

A few questions have been raised in the pool industry recently about pool water treatment. These include whether trichlor is inherently bad for pool plaster, what the effect of cyanuric acid is on pool plaster, whether pools can successfully be chemically maintained with weekly service visits, and what, if any, improvements have been made to water balancing chemistry in the last 40 years.Trichlor – Because of its ease of use and its stability in storage, trichlor use has increased in popularity. When using trichlor for chlorination, very little if any muriatic acid is needed for pH reduction, as compared to the need to use a significant amount of muriatic acid when using bleach or cal hypo.The advantage of using trichlor over having to add liquid acid (and even dry acid) is that it dissolves very slowly, which allows the water to buffer (resist pH change) the moderately acidic nature of this chemical much easier. Both muriatic acid and sodium bisulfate (dry acid) dissolve quickly, and immediately pack a significant punch in lowering pH. Since muriatic and dry acids are heavier than water, they sink to the bottom of pools when added improperly, which is aggressive to the plaster surface. More importantly, muriatic and dry acids are one hundred times more acidic than trichlor. That is certainly something to be considered. When added by hand, liquid and dry acids should always be diluted and trickled around the perimeter of the pool.Because of the slow dissolving nature of trichlor, another advantage of using it is that it helps maintain a more consistent pH over the course of a week. While treating swimming pool water, we all have learned that the pH in typical pool water generally rises after treatment and balancing. So when service techs balance pH to 7.4 when using liquid bleach and acid, and return a week later to treat the water again, the pH may have risen to as high as 8.0. However, when slow-dissolving trichlor is used for chlorination (instead of bleach or cal hypo), the slow dissolving of trichlor (which is moderately acidic) will offset this natural pH rise over the course of a week and will help maintain a more constant pH during this time period. So as one can see, there are certain advantages of using trichlor.While improperly fed trichlor (that is, when trichlor is allowed to concentrate rather than dissolve in a distributed fashion) can cause etching on a top step or corner of a pool or at a return line opening, blaming trichlor for other, non-etching related plaster problems, especially in other areas of the pool, is misguided.Cyanuric acid – This chemical has come under recent scrutiny – both in its role as a component of the alkaline buffer in a pool, and its effect on plaster. In a nutshell, cyanurate (the alkaline portion of cyanuric acid in water) is part of the total alkalinity. When performing accurate water balance equations (SI), only the carbonate/bicarbonate type of alkalinity is supposed to be included, so the bicarbonate needs to be isolated from the cyanurate alkalinity. The APSP has published material on this process, and we recommend it. On the other hand, some claim cyanuric acid is inherently aggressive to plaster surfaces. Properly dissolved cyanuric acid at recommended pool concentrations is not aggressive, in and of itself, to plaster.Weekly Service – Some industry people have made the claim that service techs are not capable of properly maintaining balanced water chemistry with weekly service visits. In light of the fact that many have been doing that for decades, and absent any proof to the contrary by the claimants, this one doesn’t really deserve further comment, other than to perhaps point out that the increase in automation, the use of Trichlor mentioned above, and the use of cyanuric acid, make this claim even further from the truth.Advances – Let’s look at a few other advancements in the maintenance of pools over the years. Before the mid-70s, test kits usually only included pH and total chlorine tests, while testing for alkalinity and calcium hardness was almost non-existent. Now, test kits, including test strips, are more sophisticated which includes testing for alkalinity, and hardness. Mini spectrophotometers are now available for more reliable readings. Mini labs are available for very accurate titration capabilities.Back in the 1970’s, the concept of water balance (Langelier Saturation Index) was not widely known or understood. Now, balancing water using the Saturation Index is now expected of both professionals and pool owners. Very recently, the Saturation Index has been modified and improved because of high TDS considerations. Chemical addition charts have been developed and improved providing more accurate amounts of chemicals to add for balancing. Computer software programs provide pool stores with the ability to assist pool owners in water balancing.The service industry today has special chemical startup procedures, chelation and sequestering agents, and stain removal programs. Research has shown optimal methods of chemical addition. For example, 15 years ago onBalance published its research demonstrating the fallacy of “slugging” liquid acid into pool water (for extra alkalinity reduction), and more importantly, demonstrated that it is also detrimental to pool plaster. onBalance also improved the accuracy of the original chemical dosage charts published before 1990. Devices have been introduced to slowly add chemicals and the use of automation has blossomed over the last couple of decades. Even greater advancements have come from the development of automatic pool cleaners and more sophisticated filtration systems.There has been an increase in educational seminars throughout the country, teaching and helping service techs to better understand the proper applications and mechanics of water chemistry maintenance. Trade associations such as IPSSA, UPA, APSP, FPSIE, and NSPF, with their courses and requirements for certification have been a major factor in the improvement of overall service quality.In conclusion, the service industry is providing a higher quality of pool maintenance today. We believe that there will continue to be improvements and advancements within our segment of the industry.onBalance is a consulting group comprised of Que Hales, Doug Latta and Kim Skinner

Pool ACIDS

Posted by Kim Skinner on July 15, 2009 at 9:12am

There are some differences between muriatic acid (HCl), dry acid (sodium bisulfate, NaHSO4) and sulfuric acid (H2SO4) in the treatment of swimming pool water. We will attempt to review and clarify these three types of acids.When added to water, all three of these acids increase the amount of hydrogen ions (also known as hydronium ions) present in water. These hydrogen ions immediately react with alkaline components in pool water such as bicarbonate (alkalinity) ions and convert them into carbonic acid, thus reducing the alkalinity in the water and lowering the pH. Also, when added, these three acids add a byproduct to the water. With muriatic, it is the chloride ions (Cl), with dry acid and sulfuric acid, the bi-product is sulfate (SO4) ions.Muriatic acid (also known as hydrochloric acid) is probably the most common and most used type of acid for lower pH and alkalinity in pool water. The strength that is purchased for pool water use is normally 31.45%, but sometimes is marketed at 20% and even 10% in supermarkets and hardware stores.Dry acid (sodium bisulfate) has become more popular in recent years, probably because it is a little easier and safer to use. Its strength is usually about 93-94%. But don’t let that fool you. While sodium bisulfate may have a higher strength percentage, it still costs more to use than muriatic acid. For every gallon of muriatic acid, it requires about 10.5 lbs. of sodium bisulfate to do the same job. While the cost varies depending volume purchased and other factors, if muriatic acid is about $3 to $4 per gallon, that would be compared to 10 lbs. of dry acid that costs about $8 to $12, perhaps more.Some service techs use sulfuric acid to lower pH and alkalinity and also for acid washes. There is a general understanding that sulfuric acid may remove copper stains more effectively than does muriatic acid. The typical strength for sulfuric acid purchased in one gallon containers is around 38%. While the percentage strength of sulfuric acid (38.5%) is higher than muriatic acid (31.5%), they are nearly equal in pH and alkalinity reduction gallon for gallon. So the price per gallon between the two acids may be a deciding factor when considering which to use.There is the possibility of purchasing a higher strength sulfuric acid in bulk containers which has the strength of 93% or higher. This high strength acid is about 3.5 times stronger than muriatic acid. So price wise, using this high strength sulfuric acid would save money. However, one problem with using 93% sulfuric acid is that it is more hazardous to use. It is extremely corrosive, more so than muriatic acid and sodium bisulfate.Also, other potential problems to consider when using sulfuric acid (including sodium bisulfate) is that they add sulfates to the water. In time, the content of sulfate increases in the water, which then can combine with calcium ions and form a precipitate crystal. Calcium sulfate deposits can be particularly difficult to remove from pools. Regular acid washes do not have much of an effect on removing this deposit. High sulfate contents in pool water can also be harder (more corrosive) to cement finishes.The following are formulas on how much of the three acids to add for lowering alkalinity.For muriatic acid, it is Volume (of the water) divided by 125,000 then multiplied by the ppm desired reduction in alkalinity which then gives the amount of QUARTS to add.For sodium bisulfate (dry acid), it is Volume divided by 47,000 then multiplied by the ppm desired reduction in alkalinity which then gives the POUNDS to add.For 38.5% sulfuric acid, it is Volume divided by 128,000 then multiplied by the ppm desired reduction in alkalinity which then gives the QUARTS to add.For 93% sulfuric acid, it is Volume divided by 432,000 then multiplied by the ppm desired reduction in alkalinity which then gives the QUARTS to add.

Soda Ash versus Bicarb - Equal?

Posted by Kim Skinner on July 2, 2009 at 9:17am

For many years there has been a misunderstanding in the swimming pool service industry about the chemical differences between using soda ash (sodium carbonate) versus bicarb (baking soda or sodium bicarbonate) to adjust pH and alkalinity in swimming pool water.The misinformation being taught in some seminars varies. Some seminar instructors claim that soda ash and bicarb, pound for pound, add equal amounts of alkalinity to pool water while raising the pH differently; while others claim that bicarbonate actually increases the alkalinity more than soda ash! Another inaccurate claim is that sodium bicarbonate will always increase the pH somewhat.SODIUM BICARBONATEA 1% solution of sodium bicarbonate in water has a pH of 8.4. Therefore, when bicarbonate is added to water having a pH less than 8.4, it will cause the pH to rise towards 8.4. Conversely, and what is not understood by some, is that if the water’s pH is greater or higher than 8.4 (which does occur occasionally in swimming pools), adding bicarbonate to this water will slightly decrease the pH down, towards 8.4. This means that in new plaster pools, when the pH often soars to very high levels, adding both acid and bicarbonate will reduce the high pH found in these new pools. By adding bicarb with acid, the alkalinity can be kept at appropriate levels, and balancing after startup will be quicker and easier. If the alkalinity is already high in a new pool, then only acid is needed to lower pH – which also lowers the alkalinity.In general, adding sodium bicarbonate will not affect the pH significantly, since the starting pH is not significantly distant from 8.4 to begin with. However, the further the pH of the water is from 8.4 to begin with, the more effect bicarb will have on shifting the pH. More importantly, the amount and the type of total alkalinity present in the water will also determine the amount of pH change when bicarbonate is added to water. The rule here is that when total alkalinity is low, it will have a greater effect on the pH from the addition of sodium bicarbonate. For example, if sodium bicarbonate is added to one pool that has a pH of 7.0 and an alkalinity of 20 ppm, and also added to another pool that has a pH of 7.0 but with an alkalinity of 100 ppm, then the greater pH increase will result with the pool that has alkalinity of 20 ppm. This is due to the greater pH buffering (resistance) of water with higher amounts of alkalinity.SODA ASHA 1% solution of soda ash in water has a pH of approximately 11.4. Because of this high pH condition, soda ash will raise the pH in water more significantly than will sodium bicarbonate. And just as with bicarbonate, soda ash will also more significantly increase the pH when a lower alkalinity level exists in the water because of the lack of sufficient buffer.Contrary to some information, soda ash also adds more alkalinity than bicarb. The amount of alkalinity contributed by soda ash is about 58.5% more than sodium bicarbonate, or in other words sodium bicarbonate is only about 63% as strong as soda ash in terms of increasing alkalinity.So what does all of this mean? Well, first it means that if you only need to raise alkalinity but the pH is okay, it is better to add bicarb because it will contribute the alkalinity needed without affecting the pH very much. If you need to raise the pH but the alkalinity is okay, then adding soda ash is best. But don’t assume that the alkalinity won’t go up, it will. You just hope the alkalinity won’t go up too much. Generally, do not add more than 4 pounds at a time per 20,000 gallons.And if you need to raise both the pH and alkalinity, then pound for pound you get more “bang for your buck” with soda ash, and it is cheaper too. But be careful. Adding too much soda ash will often cause the precipitation of calcium carbonate which results in cloudy water.

Laying to Rest the Acid Column Myth #2 of 2

Posted by Kim Skinner on June 25, 2009 at 1:36pm

Now – what really happens when acid is added in a concentrated fashion to a pool? Since acid is noticeably heavier than water, the acid sinks to the bottom, and flows to the lowest part of the pool. If that lowest part happens to include an operating main drain or an operating suction-side cleaner, the concentrated acid dose winds up in the circulation system. Although the movement of the water will eventually dilute and blend the acid into the rest of the pool, the initial contact of concentrated acid can potentially etch the plaster it touches, and attack the circulation system it flows through. Even adding several smaller “slugs” of concentrated acid will result in this puddling of acid on the bottom – try adding dye to your acid and watch it. Its fun – as long as you are not worried about etching the bottom of the pool!Of course, etching the plaster and eating the components of the circulation system is generally considered a bad thing… yet the proposed treatment process (“slugging” the acid) recommends this potentially damaging treatment technique, all for the sake of a theoretical, unfounded attempt at chemistry manipulation. Even if it worked (which it doesn’t), would it be worth the risk?What is the right way? The best way to manually add acid to a pool is to pre-dilute the acid and to add it by “walking” it around the perimeter of the pool, pouring it evenly, close to the surface, and slowly enough to minimize splashing. When added in this fashion, the acid blends throughout the pool water faster, and the pool is protected from low pH. In fact, in extensive testing of the two methods, pH levels at the bottom of the pool with the “slugged” method were routinely below 3.0. In pools treated with the acid dilution and distribution method, the lowest pH levels measured next to the plaster were in the 7.1-7.2 range. (Repeat – once the acid addition was blended throughout the water, the end-result pH and total alkalinity reduction was identical, no matter how the acid was added.)After having conducted experiments in 1994 and documenting that the acid column program was an incorrect concept, all but one of the major sources we cited have revised their publications and removed the myth from their recommendations. The remaining hold-out, unfortunately, is widely read and refuses to change – not based on science, but because they claim that service techs in the field think the acid column works!It is time to get this nonsense laid to rest, and stick to what is scientifically sound and that we all know works. There are proven ways to preferentially affect pH and alkalinity, and there are proven treatment strategies for pools that don’t want to follow the pH and alkalinity norms. Let’s stick to them, and quit risking damage to pools in our care.Here is a photograph sequence of an acid column in action. The pictures were taken with an underwater camera, and the acid was colored with phenol red powder... the same chemical used to test pH. Unless the circulation system is running, or the unless the resultant puddle of acid on the bottom of the pool is brushed or moved around some way, the puddle will stay visible and intact for hours – with a pH of about 2.5 right on the plaster. Ouch!

Laying to Rest the Acid Column Myth #1 of 2

Posted by Kim Skinner on June 25, 2009 at 9:29am

Although it has been fourteen years since onBalance (Que Hales, Doug Latta, Kim Skinner) first debunked the Acid Column Myth in the Journal of the Swimming Pool and Spa Industry, we still regularly get asked in our trade show chemistry classes about its validity. As recently as this year’s shows we found the need to re-debunk the concept, while another instructor in another class continued to teach it as valid… without any supporting facts. Why has this incorrect and potentially pool-damaging practice so persistently managed to survive? We would like to recount what the myth is, why it is wrong, why following the practice could damage your pools (costing you money), and why the idea still seems to refuse to lay down and die.First, the myth. As we mentioned in the 1995 research journal article, at that time many pool industry publications promoted this (faulty) method of preferentially lowering pH and/or alkalinity:– That if acid is added by walking it around a pool and evenly distributing it throughout the water, the pH will be preferentially lowered, with only a minor decrease of alkalinity.– And that if acid is poured in a concentrated area, variously referred to as a column, slug, well or cloud, the alkalinity will be drastically reduced, but the pH will not drop as much as it otherwise would.Various attempts have been made to develop a chemical rationale for why this is supposed to work. As can be expected (since the whole idea is a myth...), none of the attempted explanations are valid science, nor are they what actually happens in a swimming pool.Most of the rationales center around the (mistaken) assumption that lowering pH decreases carbon dioxide (CO2) solubility – in other words, that lowering the pH enough will make more CO2 escape into the air. The fact of the matter is that pH is not a solubility factor for CO2. The actual things that govern CO2 solubility are temperature, pressure, and agitation (exposure to air).The easiest way for the non–chemist to remember these factors is to think of a can of carbonated beverage, such as soda pop or beer. The colder the can, the more fizz (CO2). The higher the pressure, the more fizz... opening the can and leaving it sit loses fizz. And shaking the can decreases fizz, by releasing CO2 gas from the liquid into the air. If anything, lowering the pH of “flat” or “stale” soda by adding dry ice (frozen CO2) increases the CO2 content – just ask anyone who has made home-made root beer!The plain and simple fact of the matter is that a given amount (or “dose”) of acid added to a fixed volume of water (the pool) will result in an identical reduction of both pH and alkalinity. Every time. No matter how it is added. That’s the rule, that’s science, and it can easily be demonstrated at poolside by anyone with a test kit. The only real chemical difference between the two addition methods is the time required for the acid to blend throughout the entire pool.

A Deeper Look at Alkalinity #2 of 2

Posted by Kim Skinner on June 19, 2009 at 9:42am

It should be understood that neither low total alkalinity (below 60 ppm) nor higher levels than 180 ppm will detrimentally affect the efficacy of chlorine or other types of sanitizers. As long as the pH is in the range of 7.2 to 7.8, the sanitizer will still be able to effectively destroy bacteria and algae and keep the pool safe to swim in. Unless the pool is cloudy, there is no need for Health Inspectors to close the pool just because the alkalinity is out of range. As mentioned above, simple steps can be taken to correct the out of range alkalinity content.The one unfortunate aspect regarding alkalinity is that when total alkalinity is in the proper operating range of 60 ppm and 180 ppm, it causes the pH to seek a natural level of about 8.0 to 8.3. Consequently, acid is needed to constantly lower the pH back to the operating parameters of 7.2 to 7.8. Periodic additions of sodium bicarbonate are needed to replenish the alkalinity lost due to acid addition. Another approach to pH control is to add carbon dioxide, rather than acid, for pH control. In such a case regular alkalinity replenishment may not be required.Adding carbon dioxide lowers the pH, but does not affect the total alkalinity content. The loss of carbon dioxide increases the pH toward 8.4, and also does not affect total alkalinity.If pool water contains cyanuric acid (from the addition of Trichlor and Dichlor, or from direct additions), it also contributes to the total alkalinity. This is why the term “total alkalinity” is used when discussing pH buffering capabilities and for establishing the minimum and maximum levels. However, the alkalinity contributed by cyanuric acid is not a “carbonate” type of alkalinity, which is the type of alkalinity needed to determine proper water balance using the Langelier Saturation Index (LSI). “Carbonate” alkalinity consists of bicarbonate and carbonate ions. Sodium bicarbonate, sodium carbonate, and sodium hydroxide are chemicals that can be added that contribute to “carbonate” alkalinity.

A deeper look at Alkalinity #1 of 2

Posted by Kim Skinner on June 15, 2009 at 6:51am

A Deeper Look at AlkalinityOf all water balance parameters, “alkalinity” may be the least understood. Alkalinity is what helps maintain a proper pH (from 7.2 to 7.8), and buffers, or resists wild pH fluctuations when sanitizers or other chemicals are added to pool water.Sanitizers, when added to water, in addition to providing chlorine, also have an acidic (acid or low pH) or an alkaline (basic or high pH) effect on the water. It is the alkalinity (primarily in its bicarbonate form) that reacts with and “absorbs” the pH-altering effect of the sanitizer. This process “buffers” the pH, but may also either add to or lower the total amount of alkalinity in the water. Adding other types of chemicals also may have an effect on pH, and those effects are also “buffered” by the alkalinity.The APSP has established that pool water should have a minimum of 60 ppm and a maximum of 180 ppm of total alkalinity. If the total alkalinity is below 60 ppm, there may not be enough alkalinity (buffering capacity) to resist a significant pH change if an acidic or basic chemical is added. In the case of adding an acid, the pH could drop below 7.0, making the water very corrosive to pool plaster, metal fixtures and equipment, as well as being very irritating to swimmers’ eyes. In the case of adding a high pH (alkaline) chemical, the pH could go excessively high (over 8.3), which increases the likelihood of calcium carbonate (scale) depositing onto the pool surface and equipment.The reason for a maximum level of total alkalinity is due to the fact that a level higher than 180 ppm also increases the possibility of scale forming. An exacerbating factor is that higher bicarbonate alkalinity can cause a more rapid upward drift in pH, due to the gradual loss of carbon dioxide from the water. It should to be understood that an alkalinity below 60 ppm or above 180 ppm does not necessarily mean that a corrosive or a scaling condition is imminent, only that the possibility of this condition is more likely. Other water balance parameters such as pH, calcium, and temperature may be able to counterbalance the out of range alkalinity level, although this is not a recommended way of maintaining water balance.A low total alkalinity level can be quickly corrected by the addition of sodium bicarbonate (baking soda). Sodium bicarbonate increases the alkalinity level without affecting the pH significantly. Sodium carbonate (soda ash) also increases the alkalinity, even more than sodium bicarbonate (pound for pound). However, it may also raise the pH too high.Too high of an alkalinity level can be corrected by adding muriatic acid or dry acid (sodium bisulfate), but will take more time because the acid has to be added slowly and in small increments.Important Note: In regards to lowering alkalinity, there is NO truth to the concept that pouring acid in one spot of the pool (the column or “slugging” method) will result in a greater reduction of alkalinity than distributing the acid evenly around a pool. No matter how acid is added to the pool, it will always have the same effect on the alkalinity, as well as the pH. When manually adding acid to a pool, it is important to always dilute the acid and trickle it into the pool by walking around the perimeter. Acid is heavier than water and will sink to the lowest area of the pool, with the potential to damage (etch) the plaster surface, as well as the equipment if drawn in by the pump system. Pool operators should never pour undiluted acid into one area of the pool.

Carbon Dioxide in Pool Water #4 of 4

Posted by Kim Skinner on May 28, 2009 at 2:59pm

CO2 in Pool Water #4So how long does it take for CO2 to off-gas after adding acid? Or, why does the “rebound” happen faster in some pools than others, or faster one time than another in the same pool? CO2 off gassing, and its relative speed, are dependent on several factors, which include water temperature, circulation, total alkalinity, ratio of water volume to air-exposed surface, and atmospheric pressure. These factors affect both the rate and the percentage of either off-gassing or absorption.Factors which accelerate off-gassing (and speed pH rebound) include higher water temperatures, increased circulation, and especially increased aeration. Factors which inhibit off-gassing (thus slowing down pH rebound) include decreased aeration, decreased circulation, and low temperature. Factors which promote absorption of CO2 (which drops pH) include high total alkalinity, a pH above 8.4, and low water temperature.Service techs can easily observe for themselves the speed at which CO2 off-gasses by watching the speed at which the pH increases, or returns to normal in their pools. They will detect how some pools have a major change in the pH within a day or so, maybe even in just a few hours, while some pools take over a week to have a significant change in the pH. Obviously, however, adding any more chemicals affects the pH and the process starts all over.Another practical application relating to CO2 in water is the process of lowering high alkalinity levels in a short amount of time without allowing the pH to drop below the ANSI/APSP-recommended minimum of 7.2. The traditional methods involve either adding enough acid at a single time to remove the right amount of alkalinity (in which case the pH likely goes lower than desired), or adding smaller amounts of acid at intervals, allowing the pH to slowly rebound, and then repeating the small acid dose, over and over until the desired alkalinity level is reached, which takes hours or days.The “CO2-savvy” method is accomplished by adding acid to water while off-gassing (by increased aeration and/or increased surface exposure) as much as possible. Aeration can be accomplished by turning on venturi jets, spa air bars, or other features or devices that create air bubbles in the water. Aeration is quite effective at rapidly reducing the CO2 in the water by increasing the surface area of water to air, which is where the off gassing occurs. Increased surface exposure includes longer circulation times, and using water features such as fountains – which might not technically aerate, but still increase the total amount of water exposed to air.The routine involves adding just enough acid to lower the pH to 7.2, and then circulating and aerating the water as much as possible. The acid lowers the alkalinity, and the aeration accelerates the process of CO2 off gassing, thereby increasing the pH. Then more acid may be added, to pH 7.2, and so on – until the alkalinity reaches the desired target. In a relatively short period of time (at least, compared to traditional methods) the target alkalinity is reached without a) taking a lot of time, or b) allowing the pH to drop below safe and desirable ranges.This is the final segment on Carbon Dioxide.Provided by onBalance - Kim Skinner, Que Hales, Doug Latta

Carbon Dioxoide #3 of 4

Posted by Kim Skinner on May 21, 2009 at 8:14am

CO2 in Pool Water #3 of 4While some of the following information has already been mentioned, let’s specifically address the question raised at the beginning of this update series. Why does the pH eventually rise after acid initially makes it drop? Again, the answer lies in the fact that whenever the pH is below 8.2-8.3, there is generally more CO2 in water than its natural equilibrium level with the atmosphere. Because of this, the extra CO2 will off-gas into the atmosphere over time. The pH rises because CO2 is off-gassing from the pool water. Unless checked, the pH will continue to rise until the CO2 reaches its equilibrium or about 8.3. The more alkalinity (over 80 ppm), the stronger pull to a pH of 8.3. This is one of the difficulties that pool service techs have to deal with. Generally, there is no getting around this.But there are exceptions to the above rule. For instance, a common but occasionally unrecognized factor which interferes with CO2 off-gassing or absorption is a pool cover. When pools are covered with non-gas permeable covers, such as the common blue bubble solar blankets or solid vinyl or plastic automatic safety covers, the exchange of gas from water to air and air to water is blocked.With newer plaster pools, a vast supply of hydroxide (a component of the plaster surface) is exposed to the water and its chemistry. If a pool cover blocks the otherwise natural process of CO2 off gassing, the CO2 reacts with the plaster surface and, together with hydroxide, form carbonate, thereby reducing CO2 in the water. Eventually, all aqueous CO2 could be depleted, causing the pH to climb to 8.4, and the pool cover would not allow more CO2 from the atmosphere to dissolve into the water to keep the pH from rising even higher than 8.4. At this point, dissolved calcium in the water would probably begin to precipitate and produce scale on the floor and walls.In vinyl, painted, and fiberglass pools, on the other hand, no ready source of hydroxide is available, so pool covers on these pools can keep the pH artificially low when inhibiting the ability of CO2 to off-gas. When acid or an acidic sanitizer is added to this type of pool that has a non-permeable cover on it, the CO2 generated (by the acid) will stay in the water, and will not be able to off-gas. Therefore, the pH will probably remain low and unchanged until either other chemicals are added, or the cover is removed.When non-permeable covers are used, pH needs to be watched carefully. Ideally, the cover should be removed for enough time to allow gases to equilibrate (perhaps 6 to 8 hours, twice a week for residential pools). When this is not an option, careful control of pH using acids and bases must be maintained. How will you know if the pool contains the right amount of CO2? The pH will be balanced.

Carbon Dioxide in Pool Water #2

Posted by Kim Skinner on May 16, 2009 at 1:26pm

After adding acid to the pool water, the pH goes down (at first) because of the effect on pH of the increasing amount of CO2 (aq) produced by the acid. Shortly afterwards, the pH begins to rebound and eventually can return to its original level. This is due to the equilibrium relationship between the amount of CO2 in the water and the amount of CO2 in the air above the water. This is known as Henry’s Law. Since the acid addition forms more CO2 (aq) in the water than is dictated by the equilibrium, most of the CO2 (aq) created by the addition of acid will then begin to release and off-gas into the atmosphere – which will gradually raise the pH level but not the alkalinity.It may be instructive at this point to mention that the “natural” level of CO2 in balanced pool water after it has had sufficient time to reach equilibrium with the atmosphere is from about 0.5 ppm to 2.0 ppm and the pH will be around 8.0 to 8.3. This pH range is dependent on total alkalinity.Since it is dissolved CO2 in water that keeps calcium soluble in water, we want to maintain pool water with just enough CO2 to keep the pH down in the mid to high 7 range. Too much CO2 in water creates low pH conditions that are aggressive to pool plaster, and no CO2 creates high pH conditions that are scale forming to pool surfaces. Of course, etching and scaling are something service techs are always trying to prevent from happening.CO2 can also be added to pool water by simply injecting pure CO2 into the water, or by adding “dry ice” (frozen CO2) to water. The pH will drop, and if a large amount of CO2 is absorbed into the water, the pH could go below 6.0. Despite the fact that the pH could be lowered dramatically, no change or reduction will occur in the alkalinity under this scenario. This fact bears repeating because it is incorrectly being taught in some seminars. The amount of CO2 in water does not affect the content of alkalinity, only the pH is affected.The process of injecting CO2 into water (especially spas) is becoming more and more popular. Systems have been designed to add CO2 into the water when sanitizers such as bleach are used. The concept behind this is to use CO2 to offset the high pH effects of bleach. This system works quite well to keep the pH in check and in balance (7.2 – 7.8) except for the fact that the total alkalinity will gradually increase over time, but this is only due to the small amount of alkaline properties of the bleach, not the CO2.Therefore, small amounts of acid will eventually need to be added to control total alkalinity levels, and it won’t be necessary to experience the vicious cycle of adding larger doses of acid followed by offsetting doses of sodium bicarbonate or soda ash to maintain pH and alkalinity. But, because the content of the CO2 being injected in the water is higher than the natural level (equilibrium, or 8.2-8.3), most of it will off-gas over time. Therefore, a continual addition of CO2 will be needed to keep the pH from rising. Although this may be done manually, it is much easier by dosing the CO2 with a pH controller.

Carbon Dioxide in Pool Water

Posted by Kim Skinner on May 14, 2009 at 4:22pm

The Role of CO2 in Pool Water #1While some service techs go about their business taking care of various swimming pools, and specifically after they lower pH by adding acid, they may ask themselves why the pH of the water begins to rebound (rise back up again) afterwards. Also, they may wonder why this pH rebound happens faster in some pools than in others.The answer lies in the behavior of carbon dioxide in the water. Carbon dioxide (also known as CO2 & carbonic acid) is formed when acid is added to swimming pool water, and it is this compound that affects the changes in pH of pool water.Carbon dioxide (CO2) is a common, essential compound in nature. It is found almost everywhere, from what flowers and trees breathe in, to what humans and animals breathe out; and to the bubbles in the soda you drink. In its warmer phase it is a gas, and in its colder phase it becomes a solid – dry ice. Our atmosphere (the air we breathe) contains a relatively small amount of gaseous carbon dioxide – only about 0.03% to 0.06% – which is fortunate, since levels around 10% or higher would cause us all to lose consciousness! Because it exists in the air, a slight amount of carbon dioxide can be absorbed by water.In water, CO2 primarily exists as aqueous CO2 (gas in, but not fully reacted with the water), but a small amount also combines with water to form carbonic acid: CO2 + H2O = H2CO3, and the slightly acidic nature of this compound lowers the pH somewhat.Carbon dioxide plays an important role in the make up and balancing of pool water. When dissolved in water, carbon dioxide has a direct effect on the water’s pH. The more CO2 in the water, the lower the pH, and the less CO2, the higher the pH. Pool water with no dissolved CO2 (and with a minimum alkalinity of 100 ppm) will have a pH of about 8.4 (as long as no other chemicals have been added). On the other hand, pool water that is saturated with CO2 will have a pH down around 5. Rain water can pick up CO2 (acid rain) from the air which affects pool water by lowering the pH.Although CO2 can be introduced to water from the air, it is also produced in pool water by simply adding acid. As we all know, when acid is added, both the alkalinity and the pH are lowered. The alkalinity is lowered because, with normal pool water parameters, the added acid reacts with bicarbonate alkalinity in the water, converting it to carbonic acid and aqueous CO2 – which is then no longer alkalinity.For you who enjoy formulas, bicarbonate and acid form carbonic acid and chloride, or HCO3 + HCl = H2CO3 + Cl, and then all but a fraction of a percent of the carbonic acid shifts to aqueous CO2: H2CO3 <==> CO2 (aq) + H2O. Depending on the amount of acid added, a specific and calculatable amount of alkalinity is eliminated.