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The Journal of the Swimming Pool and Spa Industry is coming back! JSPSI, a peer-reviewed technical journal, began in 1995 as a subscription-supported print-based publication. It contained articles at a technical level, of interest especially to the more experienced members of the industry. The Journal discontinued publication in 2004, primarily due to the printing, binding and postage costs associated with a print journal.

A technical journal differs from other trade publications in that it contains no advertising, is not for profit, and is peer reviewed, a process where submitted articles are blind reviewed by experts in the specific field, and are selected based on appropriateness and scientific accuracy. Authors range from consultants to chemical manufacturing technical departments, from experienced tradesmen to trade organizations.

All previous articles from the old Volumes 1 through 5 are being prepared and posted to the website.

Que Hales, the Editor, has announced that the Journal will be revived as a free, online publication. JSPSI will still be laid out in a format suitable for printing and binding, but in a pdf format so readers may view articles online or print them for later reference or study.

This first new issue, Volume 6 Number 1, includes articles on chlorine, buffer, and cyanuric acid chemistry, and is available now by going to www.poolhelp.com and clicking JSPSI. Additional issues are expected to appear biannually. New submissions to the Journal may be addressed to que@poolhelp.com.

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In Kim’s blog post on plaster mottling, Mitch Brooks, the Executive Director of the National Plasterers Council, made the comment “We solve issues...not point fingers which is what you guys love to do!” For those of you who have been on the short end of the NPC’s collective finger, or specifically the finger pointed by the NPC’s Technical Director, Greg Garrett, that comment by Mr. Brooks sounds pretty incredible. For those of you who are unaware of the type of finger pointing Mr. Garrett engages in, consider the following:

In April of 2001 Greg Garrett associated what he called “spot etching” and “highlighting” with aggressive water chemistry (pool in Phoenix AZ – see oB-00004). He also specified that there was no responsibility on the plasterer involved. The professional laboratory analysis then showed that the real culprit was the plastering company and its workmanship.


In August of 2003 Greg Garrett associated mottled white discoloration of colored plaster with aggressive water chemistry (pool in Tracy CA – see oB-00005D). He also specified that there was no responsibility on the plasterer involved. The professional laboratory analysis then showed that the real culprit was the plastering company and its workmanship.


In August of 2003 Greg Garrett again associated almost total white discoloration with aggressive water chemistry (pool in Livermore CA – see oB-00005E). He also specified that there was no responsibility on the plasterer involved. The professional laboratory analysis then showed that the real culprit was the plastering company and its workmanship.


In August of 2003 Greg Garrett also associated patterned white spotting of colored plaster with aggressive water chemistry (pool in Tracy CA – see oB-00005M). He also specified that there was no responsibility on the plasterer involved. The professional laboratory analysis then showed that the real culprit was the plastering company and its workmanship.


In December of 1994 Greg Garrett associated spot etching with aggressive water chemistry (pool in Phoenix AZ – see oB-00019). He also specified that there was no responsibility on the plasterer involved. The professional laboratory analysis then showed that the real culprit was the plastering company and its workmanship.


In August of 2007 Greg Garrett associated “etching, highlighting, and associated discoloration” with aggressive water chemistry (pool in Highland CA – see oB-00040). He also specified that there was no evidence of improper workmanship on the part of the plasterer involved… even though the plaster had delamination and cracking though which the gunite could be seen beneath, and the plaster subsequently began to literally fall of the side of the pool! The professional laboratory analysis showed that there was no evidence of any etching. Of course the real problem – massive delamination – was indeed a result of substandard workmanship on the part of the plastering company.


In September of 2009 Greg Garrett associated mottling discoloration with aggressive water chemistry (pool in Tarzana CA – see oB-00044). He also specified that there was no responsibility on the plasterer involved. The professional laboratory analysis then showed that the real culprit was the plastering company and its workmanship.


This is just the tip of the iceberg. I have only included examples of pools where I have both written evidence of Mr. Garrett’s statements and a professional failure analysis lab making a determination on the same pool. But Mr. Garrett is making a cottage industry of visiting pools and blaming water chemistry when the actual causes are known mixing, placement and curing defects documented in conventional cement/concrete science. I have read many, many more reports written by Mr. Garrett that are along the same lines.

In many of these cases, Mr. Garrett was involved specifically on the recommendation of the National Plasterers Council. He is, after all, their Technical Director. But keep in mind that this isn’t just a pattern of making incorrect assessments – these are real pools where real pool owners and/or service techs were put at risk for replastering pools when the fault lay with the plastering contractor.

Now, I understand that Mr. Garrett, as well as onBalance partners, specifically visit pools where the whole point is to make a determination as to causation and responsibility. But it has always been our understanding that such determinations should be based on fact and science, rather than apologetics.

Feel free to click on the links in this blog and see the comparison between onBalance determinations and Mr. Garrett’s. I hope these examples illustrate the absurdity of Mr. Brooks’ claim that it is onBalance that is “pointing fingers.”

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Comments on the NPC Technical Manual

As we have mentioned in previous communications, we are concerned about the continued trend in the industry to micromanage some parts of the industry while rejecting even reasonable management of other, equally critical parts.As we meet with pool owners at the water’s edge we are frequently concerned about the unreasonable standards some representatives of the pool plastering community expect of the water chemistry – and the lack of any standard relative to some plastering parameters.At one time, I and other service technicians were active members of the National Plasterers Council’s Technical Manual Committee, and that manual could have been a vehicle for improving the performance of those plasterers needing more guidance. Unfortunately, the powers that be at the NPC did not approve of our input, and in preparation for the 2002 Edition they removed us from the committee. Since that time it is our opinion that the manual has steadily decreased in quality. While the majority of pool plasters continue to do good work, the minority doing poor work can and do use the manual as a shield over their substandard work. (If one can call the manual a standard…)The current (2009) edition of the National Plasters Council’s (NPC) Tech Manual contains incorrect statements, claims, or omissions of important workmanship issues for the making of a quality pool plaster product. The misinformation in the current 2009 manual misleads plasterers on proper workmanship concepts, and enables them to avoid responsibility for sub-standard work and poor quality pool plaster. Clearly, the NPC Tech manual it is not the main-stay of accepted practices as they claim.Pool plaster is similar to concrete and cement flatwork. Pool plaster uses the same kind (Type I) Portland cement used in concrete flatwork. The large aggregate in concrete is tamped down below the surface, and the cement and sand fines rise to the surface, which then is troweled just like pool plaster. Since pool plaster is only half an inch thick and is troweled to a very smooth surface (more so perhaps than most cement flatwork), and given the environment it is to be subjected to, it is even more critical to follow appropriate practices and guidelines for a durable and aesthetically pleasing cement finish in the pool environment than sidewalks, driveways, slabs, and even decorative concrete applications. Yet amazingly, when it is shown to the NPC that improper practices can lead to early deterioration or cosmetic defects, the NPC suggests that concrete studies (ACI and PCA) and our (onBalance) studies on pool plaster don’t apply to them. That is obviously not the opinion of the concrete industry as a whole.It is fascinating to us that the Technical Manual is prefaced with the statement: “Unsubstantiated theories” which do not have significant scientific data to support their position, or any conjecture that serves only to mislead the general public, will not be considered herein.” (Sixth Edition NPC Technical Manual, 2009, on page 3 under QUALIFICATIONS).- Let’s see how well this statement is adhered to by this Tech manual.Section 2.4 – WaterThe NPC Technical Manual contains no standard for a maximum water-to-cement ratio. Both ACI and PCA literature mentions the importance of not allowing too much water to be added to cement products that require a durable surface. They set a general limit of 0.50 w:c, or a weight of water equal to half the weight of the cement for durable concrete. A high amount of water (wet mix) leads to severe craze cracking and “dusting” (similar to plaster dust forming in new pools). Not setting a limit allows plasterers to rationalize adding too much water, and not being held responsible for the defects caused by a high water-to-cement ratio. We recommend a maximum ratio of 0.48 pounds of water to one pound of cement.Section 2.5.1 – Calcium ChlorideThis section of the Manual states that the addition of 1% to 2% calcium chloride provides increased strength to cementitious products at an early age (one week), while not mentioning that the long-term durability can be negatively affected, which is the more important issue. Also, the wording states that “the 2% limit may not be critical to swimming pool plaster.” (This wording was added beginning with the 2005 edition). We disagree and there is ample cement literature and studies by the ACI and PCA that document the negative effects of adding calcium chloride, especially in excess. The Tech manual should caution plasterers against using too much calcium chloride in their mixes.Section 4.3.1 – Mix WaterThis section does not set a maximum amount of water that can be added to a mix. (See Section 2.4 above)Section 4.3.2 Lubricating WaterThis section incorrectly suggests that it is appropriate and acceptable to add water to a hardening plaster surface while it is still being troweled and finished. According to the ACI and PCA, it is not acceptable to add water while troweling cement flatwork due to possible discoloration and durability issues. While important with white plaster, this especially applies to colored plaster.Section 6.2.2 – Closed shrinkage CracksThis section does not mention that both high calcium chloride and high water additions to the mix are possible causes of severe or excessive craze cracking (closed shrinkage cracks).Section 6.3 – Inferior MaterialsThis section does not acknowledge that excess calcium chloride additions are a possible cause of an inferior surface and reduced durability as documented by the ACI and PCA.This section does not mention that adding water while troweling can be a cause of inferior surface strength and durability, and doesn’t mention that applying water to the surface or to tools during finishing leads to discoloration problems, and porous surfaces, causing streaking and mottling discoloration as documented by the ACI and PCA. An inferior or porous surface can not be remedied short of replacement.Section 6.4 – Debonding and DelaminationsIn discussing this problem, the 2009 Tech manual omits that “nodules” (also known as “calcium nodules”) are a symptom of delamination and bond failure (or also crazing). Yet the1998 Tech manual acknowledged this phenomenon and correctly stated that the responsibility is with the plasterer or those who prepared the surface prior to plastering. Plasterers are now blaming this problem on improper water chemistry.Section 6.4.2 – Buckles, blisters, and spallsThis section incorrectly suggests that “aggressive pool water chemistry” can lead to spalling and delamination. This is false. In fact, the earlier 1998 Tech manual acknowledged that improper finishing and mixing can lead to flaking and spalling and “that no definitive documentation currently exists to support the claim that aggressive water chemistry causes spalling.” But the 2009 NPC Tech manual now claims that aggressive water can cause spalling and delamination! There is no documentation that identifies aggressive pool water as causing spalling or flaking of pool plaster. Yet, there is documentation from the ACI and PCA that improper workmanship (troweling) leads to flaking, spalling, and delamination.This section should also include that another possible cause of spalling can be from “adding water while troweling.”Section 6.5 – DiscolorationThis section does not acknowledge the darkening (severe mottling) effect of adding too much calcium chloride. The 1998 Tech manual did mention this, and the ACI also has documented this along with late hard troweling. However, NPC field inspectors are blaming dark discolorations on aggressive water chemistry. There is no supporting documentation that proves this claim.This section does not acknowledge that blotchy and whitening effects on dark colored plaster can result when calcium chloride is used (especially to excess), and also when adding water while troweling. Efflorescence (salt) is also incorrectly blamed for discoloration of the surface. The PCA has documented that efflorescence on a cement surface (also known as “dusting”) is the result of improper workmanship and material issues. (PCA Concrete Slab Surfaces Defects: Causes, Prevention, Repair 2001)Section 6.6 – Long-Term DeteriorationThis section does not mention that excess water in the mix, adding water during finishing, and adding excess calcium chloride can lead to early deterioration (low durability) as documented by the ACI and PCA. Insufficient fill delay can also cause deterioration.Section Aggressive chemical attackThis section incorrectly suggests that salt deposits emitting from cracks are the result of improper water chemistry (aggressive and/or scaling). This claim is false and plasterers are blaming “calcium nodules” on improper water chemistry instead of acknowledging them as symptoms of delamination, bond failure or cracks.This section also incorrectly claims that “efflorescence” is due to improper water chemistry. [See Section 6.5)Section CarbonationThis section incorrectly suggests that “carbonation” is detrimental and causes discoloration, a weakening and early deterioration of plaster, and blames various improper water chemistry conditions for this condition; when in fact, carbonation strengthens a plaster surface. Carbonation is a natural, normal occurrence and benefits a cement surface by converting the soluble compound calcium hydroxide (in the surface) into calcium carbonate (in the surface), a much more durable and water resistant compound. (Reference F.M. Lea)This section also improperly blames carbonation for blotchy and mottled discoloration, and even attributes open cracks in the plaster to carbonation. Instead, these conditions are caused by improper workmanship or material issues as documented by the ACI and PCA. Plasterers currently use the wording in this section to incorrectly suggest that incorrectly maintained water leads to “improper” carbonation.While it is correct that secondary carbonation layers (precipitated calcium carbonate scale) can discolor a surface, it is removable, where discoloration that is internal to the finished surface, created by deficient workmanship often are not.Section Aggressive Water DeteriorationThis section states that aggressive water will “deteriorate” a cement surface. Instead, the more correct term is that aggressive water will “etch” a cement surface. Deterioration is better defined as the breakdown of a defective (weak, soft, and porous) plaster surface.Section Leaching DeteriorationThis section states that “leaching” (as opposed to “etching”) is the dissolving of soluble (i.e., weak, soft, and porous) plaster material by water percolating through a plaster coating. That statement is correct only if it is understood that even “balanced” water will dissolve (leach) a weak, soft, and porous cement surface. A poor quality plaster surface (due to poor workmanship or materials) will deteriorate due to its own weakness. The water is only a transport mechanism. But this section incorrectly suggests that only imbalanced (aggressive) water is responsible for the (leaching) deterioration of a cement surface. Poor quality plaster (or concrete) doesn’t require aggressive water to deteriorate.Additional omissions by the 2009 Tech Manual1. The current manual does not advise plasterers to avoid plastering pools in extreme weather conditions and temperatures, or take precautionary steps to mitigate the detrimental effects of extreme weather conditions on cement flatwork. Curiously, the 1998 Tech Manual did advise plasterers to not conduct plastering operations when extreme weather conditions exist.2. The term “hydration” is also currently used by plasterers to blame improper water chemistry, improper startups procedures, or other problems for discolorations (graying or light streaking) that are actually caused by improper workmanship and material issues. The 1998 Tech manual properly acknowledged improper workmanship and material causes for “hydration” discoloration, while the current 2009 NPC manual does not.3. The NPC Tech Manual does not address the proper waiting time before filling a newly plastered pool with water. This is an important issue and plasterers should be warned that starting the fill water before six hours has elapsed after final troweling can result in a damaged surface which leads to early deterioration and staining.4. The NPC Tech Manual does not advise plasterers to test the tap water to assure that it is appropriate and balanced enough to be used for filling the pool. Plasterers or builder contractors should not allow “soft” fill water to enter the pool, since that can have adverse consequences and dissolve some of the fresh cement surface and make it more porous. Currently, plasterers blame the service tech for not balancing the water properly after the pool is already filled with potentially inappropriate water. This is as akin to securing the barn door after the horses have run away.5. Without any documentation, the current NPC Tech manual claims that “spot etching” (a term coined by pool plasterers, but more appropriately known as soft spots or streaking) is caused by improper water chemistry. The 1998 Tech Manual acknowledged that this theory by the NPC has not been proven. Recent research by onBalance and by some of the nation’s best independent laboratories has confirmed that spotting and streaking of plaster is a workmanship defect.6. The NPC has a “colored plaster” disclaimer (or contract) claiming that integrally colored or tinted plaster may become streaked, blotched, mottled, and crazed (check cracked or hairline cracked), conditions over which the plasterer has no control. That is false, and there are plastering steps that can be taken to prevent or minimize these cosmetic problems. Yet, when colored plaster jobs discolor, NPC members or consultants point the finger of blame on the service tech or pool owner for improper water chemistry maintenance as the cause of these issues! It is inexcusable for plasterers to not acknowledge that following good workmanship practices can avoid the problems of streaking, blotching and fading of colored surfaces, while leading to a quality, long-lasting, and more esthetic pleasing colored plaster finish.7. Interestingly, while the Technical manual contains the above errors and omissions, which can lead to poor quality plaster, the NPC is imposing their demands on the service industry to maintain pool water in a “perfect” water balance condition. In section 7.0 – Terminology, the NPC states that balanced water means only water that is within the APSP “ideal” range. This means that when the “carbonate” alkalinity is 70 ppm, it is automatically deemed “aggressive” even if the overall water parameters are balanced and the SI is 0.0 or above. Also, the long-standing LSI standard of -0.3 to +0.5 has been rejected by the NPC. And this has been decreed by the NPC without citing any supporting studies.This bogus narrowing of water chemistry parameters is being promoted by the very people who refuse to accept reasonable, scientifically validated standards on their own products and methods!8. The NPC promotes the use of more durable plaster products to sell to clients. Their reasoning is that typical white plaster with marble aggregate is inherently weak or soft, and that imperfect water chemistry and maintenance programs (which the NPIRC says are inevitable) will quickly deteriorate this “naturally” weak product. Their “solution” is the concept that more expensive quartz and pebble finishes will eliminate the problems that normally result with standard white plaster. Yet, the NPC now states that when problems or defects develop on these improved surfaces, it is still mostly likely because of improper chemistry! This agenda removes incentive for plasterers to perform quality workmanship if they are able to blame all problems (discoloration, cracking, and deterioration) on water maintenance. And obviously, plasterers will benefit by being paid to replaster the pool again and again (and much sooner than usual) with the more costly upgrade.It is our contention that this "plaster apologist / blame the water" agenda damages both the service industry and the pool-owning public. The original, lofty objective was to identify real causes of pool damage (letting the chips fall where they may – whether materials, workmanship, chemicals, or maintenance) has been left by the wayside in preference to apologetics and attempts to misdirect in order to avoid liability. We can do better than this. Really.
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Plaster Flaking or "Spalling"

When cement, aggregate (sand), and water are mixed to form pool plaster, about twice as much water is added as is needed to hydrate (harden) all of the cement. This is done because if the mix is too dry and thick, it is almost impossible to place and trowel the plaster to a smooth finish.What happens to the excess water? As the sand and hydrated, crystallized cement grains settle, the excess water rises to the surface. This process is called bleeding, and the rising water is referred to as bleed water. Bleed water then evaporates from the surface.Swimming pool plaster is commonly troweled in 3 to 5 separate passes – the early passes placing the material where it needs to go and consolidating it, and final passes creating the smooth, final surface. One of the arts or skills of the plastering trade is properly timing the troweling passes. If troweling is performed when bleed water is present on the surface, forcing bleed back into the plaster paste causes excessively high water:cement ratios in the surface finish, weakening it. Finishers learn to time the troweling passes so that bleed water is evaporated, and the surface is still workable before it hardens too much.The opposite problem of forcing too much water into the hydrating surface is allowing the surface to dry too fast. If the surface becomes too dry, with a dry “crust” on the surface but a wet paste underneath, a weakened zone can be formed just subsurface. This can happen when plastering on dry, hot days, during low humidity, in wind, etc. It can also include too much drying time between trowel passes, excessive hard troweling, and overworking the finish.If this happens, the top of the finished plaster will look fine, even for awhile after the pool is filled. However, after time this weakness is manifest by a 16th to an 8th inch layer of the surface flaking off, generally in small areas or spots. Often, these weak areas do not flake off until the pool is drained of its water and the plaster dries out.Here are some pictures of flaked pool surfaces: You can see the round indented area with the loss of plaster. This could be described as a “moon-like crater” look, or a shallow and sunken pit look. Note that the newly exposed surface (where the flaking occurred) is extremely rough and course, while the older existing surface surrounding the missing plaster area is much smoother.

The cement/concrete industry has documented this loss of a thin surface layer as a surface defect caused by improper application and troweling, (such as we have already described), and refers to it by many names, including surface flaking, buckling, blistering, scaling, or delamination. It is not referred to as spalling, since spalling is generally reserved to describe deeper delaminations. But in the pool plastering industry, the term “spalling” has become a commonly used term to describe this shallow surface loss. (We in the pool industry use the term “delamination” or bond failure to describe deeper, bond separation between new and old plaster or between plaster and the substrate; and we use the term “scaling” to describe calcium carbonate depositing from pool water onto the plaster surface…)Since the vast majority of pool plaster does not spall, blister, or flake off, we can see that most plasterers properly apply, cure, trowel, and finish the pools they plaster. Spalling is relatively rare, and when it does occur it is most commonly found on a step radius, on shallow end floors, and around the main drain – these being places where finishing can be an additional challenge for a number of reasons. The steps radiuses are occasionally over-worked to insure smoothness and straightness, and the floors sometimes get too much troweling due to being walked on by the pool finishers while troweling. Walls are rarely over-troweled.One thing that does not play a role in plaster spalling (or peeling) is water chemistry – aggressive water is not required to form spalls. In fact, as we have mentioned, the inherent weakness leading to spalling is created before the pool is ever filled with water.In disagreeing with the above statement, the National Pool Plaster Council (NPC) claims in their 2009 Technical Manual that “blisters and spalls can be caused by aggressive pool water chemistry.” Of course there is no documented research substantiating this statement in the NPC Tech Manual. In fact, a prior NPC 1998 Tech Manual acknowledged that there was no documentation for their position that aggressive water can cause spalling in swimming pools.Obviously, some pools or spas have spalling, along with an etched and copper stained plaster surface. But the mistake is assuming that the aggressive water that caused the etching and copper stains also caused the spalling. That is not the case.If aggressive water really was a factor in causing spalling or flaking to occur, then rain water (especially acid rain) would be causing this problem to occur consistently in all flat cement and concrete surfaces. Rain water has zero alkalinity and calcium hardness, with a pH below 7.0, far more aggressive than slightly aggressive pool water. Instead, we only occasionally see this problem on small, or isolated areas of concrete slabs, where nearby concrete surfaces are relatively smooth with no visible defects. This fact confirms that something other than aggressive water caused this problem since it rains everywhere (along with the documented, authoritative statements by the Portland Cement Association and the American Concrete Institute).If aggressive water caused spalling in swimming pools, we would also see aggressive etching of the exposed aggregate in the spalled pit. We don’t. And if aggressive water could cause spalling in pools, we would also see spalls on the top step of pools where a trichlor feeder has sat (creating a very aggressive condition). Instead, in that situation we see yellow acid-etched rings, not spalls. Also acid-started and acid-washed pools would be preferentially prone to spalling – but they are not.Aggressive water does not remain aggressive as it penetrates a cement surface. When aggressive water is in contact with a cement surface, the aggressive water is being neutralized as it reacts with and etches a cement surface. Aggressive water cannot affect the cement matrix below the surface and cause delamination of a layer of plaster, unless there are existing cracks on the cement surface.Unfortunately, pool owners and pool service techs are still being unfairly blamed for causing this plaster defect.
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Calcium Sulfate in Pools

When calcium ions in pool water precipitate onto tile and interior pool surfaces as a solid white crust or crystal, the most common form of precipitate is calcium carbonate (CaCO3), commonly referred to in the trade as “scale”.Calcium Carbonate scale has some specific, known characteristics, such as being soluble in acid, having a value of 3 on the Mohs hardness scale (with 1 being the softest – such as talc, and 10 being the hardest, such as diamonds).Calcium Carbonate scale is generally relatively uniform in its deposit pattern across the interior surfaces of a swimming pool or spa, although a certain amount of it will concentrate at the waterline as an evaporite.

Calcium scale that deposited over a long period of time (in what we would refer to as a “natural” process) tends to be somewhat smooth to the touch and low in profile, influenced in patterning by flow and/or porosity of the surface it precipitates onto, and colored by incorporated dirt or other suspended water impurities (see tile samples above). Calcium scale that deposits in a short period of time (usually through an environmental trigger such as high temperature, high pH, high alkalinity and calcium, etc.) tends to be totally uniform in deposition, pure white, with sharp defined crystals and rough to the touch:

An interesting (although fortunately not too common) variation to calcium carbonate precipitation is the precipitation of calcium sulfate. Calcium sulfate is chemically designated CaSO4, and is commonly called gypsum.If an appreciable amount of sulfate is found in pool water, it can combine with calcium (if also high in content) in the water and form a crystalline deposit. Sulfate can be introduced as a component of treatment chemicals. These treatment chemicals can include one type of liquid pool acid (sulfamic acid), dry granule acid (sodium bisulfate), dechlorinators (sodium sulfite and sodium thiosulfate), and even non-chlorine shocks (such as persulfates).Occasionally in some isolated parts of the country, high amounts of sulfate may also be present in tap water, generally from well or ground water.Calcium sulfate crystals which form as evaporites in pools are distinctive and different from calcium carbonate precipitates in several key ways. They are softer (only 2 on the Mohs scale), soluble in acid only if that acid is at boiling temperatures, and are in what is called a swallowtail crystal formation.Here is a pool with tile covered in calcium sulfate crystals:

You can see that the tile is almost totally obscured by the deposited crystals, but the grey plaster under water is not.Here is a close-up of that tile:

Here is a close-up of the crystals from the pool, showing the distinctive swallowtail shape:

Fingernails have a Mohs hardness of 2.5, while calcium sulfate is 2 and calcium carbonate is 3. Here is a calcium sulfate crystal that has been scratched on the side with a fingernail to show that the crystal is softer than the nail:

We also previously mentioned that “room temperature” acid will dissolve calcium carbonate, but not calcium sulfate… but that heated (boiling) acid will dissolve the sulfate crystals. Here is a picture sequence showing us sanding some of the sulfate deposition layer off the top step:

We then poured (non-heated) acid on the sulfate deposit near the sanded area, getting no reaction:

But when the acid hit the bare plaster, which contains calcium carbonate, it reacted, in the form of white effervescence:

We don’t have pictures of using the boiling acid, because we were too busy trying not to breathe the fumes… but it worked!This pool was located near a mountain mine, where the well-pumped source water had sulfate in it. Since that water was also high in both calcium and alkalinity, the regular use of dry acid also contributed to the problem.

The homeowner chose to resurface his pool with an exposed aggregate finish, so we didn’t do a boiling acid wash on the entire pool. This condition is also relatively rare, so you may never see one with calcium sulfate deposits. But now, if you do, you’ll know what you are looking at!Provided by onBalance – Que Hales, Doug Latta, and Kim Skinner
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I remember sitting in high school math class and griping along with the other students: why do I need to learn this stuff? When will I ever use this in real life? I also remember intentionally selecting English as my college major so I could avoid further math. To top that off, I ended up permanently in the pool industry!Then I found out that to determine the volume of a square, rectangular, oval or kidney pool a service tech needs to apply one of several geometric formulas. Fortunately, they are not too complicated…The funny part comes when you need to find the volume of a freeform pool. The instructions essentially say “divide the pool into rough geometric shapes, solve for those shapes, add the numbers together, and you will be somewhere in the ballpark.” Not only can this be difficult on some pools, but determining the average depth for these kinds of pools is an added challenge. Obviously a better way needed to be found.Much to my surprise, as we at onBalance were working on correcting industry alkalinity dosage charts, and debunking the “Acid Column Myth,” one of my old math lessons jumped back at me: if A x B = C, then C ÷ A = B! Or in other words, in terms of water chemistry, since a specific amount of acid or base added to a specific volume of water results in a given, specific alkalinity shift, then we can rearrange those variables and say that the amount of a chemical added, divided by the change in alkalinity, equals the water volume!The one tricky part about doing this at poolside is that to get an accurate answer you need to be able to test alkalinity to within one part per million, rather than the common 10 ppm precision of most poolside test kits. So get a glass, and add precisely 10 times as much pool water as is normally used for an alkalinity test sample. Then add enough color indicator to see it well. (Using more or less color indicator will not change the results of the test – it just helps you see the endpoint, or color transition better.) Then start adding the drops of titrant – but now each drop is 1 ppm instead of 10! This will obviously use up more titrant, but you only do this once per pool, and we promise you the test kit supplier won’t mind if you buy refills of their solutions ;0)Here is the simple field method we use:• Take a water sample of 10 times the normal amount from the pool for testing.• Add acid, soda ash, or another chemical which alters total alkalinity to the pool. Add enough to make a noticeable shift in total alkalinity – at least 10 to 20 ppm.• Write down exactly how much you used.• Wait for the chemical to completely blend throughout the water. (This time will vary from 45 minutes to several hours depending on the method of addition, the circulation, etc.)• Take a second 10X water sample from the pool.• Test the total alkalinity of the two samples (using the dilution method, or another comparable means of getting withing 1 to 2 ppm of the answer).• Find the formula number for the chemical you used from the list below.• Apply the following formula (using the appropriate formula number depending on which chemical was used):(formula number)(amount of chemical used in quarts or pounds)—————————————————————————— = Pool Volume(Number in ppm that the TA changed)Here are a couple of examples. First, if you add 5 pounds of sodium bicarbonate to a pool, and the starting TA was100 ppm and the ending TA was 116 ppm, then:(71,400 for baking soda)(5 pounds)—————————————— = a 22,000 gallon pool(116 – 100, or 16 ppm)Or if you add two quarts of acid to a pool and the alkalinity drops 12 ppm:(125,000 for muriatic acid)(2 quarts)——————————————— = a 21,000 gallon pool(120 – 108, or 12 ppm)Actually, the volumes in the examples came out to be 22,312.5 and 20833.33, but of course that is too precise – round off to the nearest 1000 gallons. The margin of error should be around 5%)Formula NumbersSodium Bicarbonate (baking soda) - 71,400Sodium Carbonate (soda ash) - 113,200Sodium Sesquicarbonate (sesqui) - 80,000Muriatic Acid - 125,000Sulfuric Acid - 126,700Sodium Bisulfate - 47,000
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