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The Zero Alkalinity Acid Treatment

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The concept of the “Zero Alkalinity” process (also known as a No Drain Acid Wash or Bath) is to make pool water aggressive enough (by adding acid) to dissolve and remove stains or scale from older cement-based plaster surfaces, including quartz and pebble swimming pools.  Unfortunately, this process generally removes some of the plaster surface material.


Assuming a total alkalinity of 100 ppm, it requires 4 gallons of muriatic acid (31.45% strength) per 20,000 gallons of pool water to reduce to zero alkalinity, and to a pH of 4.5.  That acid treatment over a 7 day period can dissolve and remove about 8 pounds of plaster material (equivalent to 50 ppm of calcium carbonate) from a fully cured surface.  So is that good or bad for a plaster pool? 


The reality is that 8 pounds of plaster material dissolved from a 20,000 gallon pool is not significant and would barely be seen under magnification.  If stains are removed that improve the aesthetic appearance of older pools, then that can be an acceptable program.  If the acid process only removes dirt and scale deposits and not calcium from the plaster itself, well, all-the-better. 


Some new white plaster pools develop a blotchy and darkened gray mottling discoloration within a few months of plastering.  Also, some new dark colored plaster pools develop a whitish and streaky discoloration soon after plastering. 

Those issues are often caused by improper plastering practices.  The chemical start-up program (performed by the pool owner or service tech) may not be at issue, but is often (incorrectly) blamed by the pool builder or plasterer. A no drain acid treatment generally does not properly resolve these type of plaster discoloration defects. Sometimes, the discoloration disappears for a few weeks, but soon returns afterwards. 


Unfortunately, representatives of the National Plasterers Council (NPC) often promote the Zero Alkalinity (No Drain Acid Bath) program as a “solution” for the above problems. But making matters worse, they advise adding 10 gallons of acid to 20,000 gallons of pool water, more than double the amount needed to reduce the alkalinity to zero ppm. That excessive amount of acid added can lower the pH to below 3.5, lower the LSI to a negative (-) 5.0, and dissolve about 20 pounds of plaster material from the surface.  (Twenty pounds of plaster material is equivalent to 120 ppm of calcium carbonate dissolved from a plaster surface which then increases the calcium hardness of the pool water).


And if adding all that acid doesn’t improve the appearance of the plaster well enough, amazingly, they advise to double the dose of acid for another week!  It removes about 40 pounds of plaster material! That treatment is absolutely detrimental to the plaster surface, and a disservice to the pool owner. It even destroys the evidence of the real cause of the plaster discoloration defect! 


That type of acid treatment causes an severely etched plaster surface that was originally smooth, which will then begin to stain easier and sooner by dirt and metals in the water after the acid treatment program has been performed.  When the pool becomes stained and aged within a year after a Zero Alkalinity treatment, who is going to be blamed?  Unfortunately, whoever is maintaining the pool water chemistry, not the plasterer.


To further undermine pool owners and service techs, the plaster industry advocates that pool water with a slightly negative LSI (-0.1 to -0.3, which is within APSP standards), is detrimental and that it will cause everything from craze cracking to gray mottling to plaster spalling (delamination). Yes, even the same gray discoloration that the so-called Zero Alkalinity process attempts to remove.  Obviously, that is contradictory and completely false.  No wonder they claim that pool plaster will only last about 7 years. But the fact is plaster will last 20 years if plastered with good workmanship and maintained properly.


That agenda enables plasterers avoid being held responsible, blame water chemistry, and get rewarded with additional work.  This injustice won’t stop until pool builders and other groups confront the plasterers. 


("No Drain Acid Wash" is a trademark of United Chemical Corporation).

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Comment by Norman Tyree on December 30, 2013 at 12:20pm


Start the new year with the few facts re plasters.

Several references are made to the use of Quartz, I don`t know of any plasters that are made from 100% quartz with one exception Armadillo Pool Quartz, some of the colored quartz used is added to anything from Marble to Silica Sand, then some of the so called Colored Quartz can be just Colored Sand, the so called colored process can be done different ways so in our industry which is really looking for the cheapest option will use what will provide some color, of course the use of Oxides are very common.

Re the Acid wash/bath method to prove how and why you should not use it put the product like Marble even Hydrazzo into a glass of acid and in now time it disappears totally.

So the adding of acid to a pool after filling can in effect ruin the plaster finish. So people down under use a watering can and acid wash the next day yes it exposes the surface and leaves it very rough.

Our industry is a in and out one with so many experts that can confuse with information that is not really relevant.

The use of Acid even dosing to adjust the PH is not good. I have seen pools where the dosing has overdosed and ruined the bottom of the pool, exposed the structure underneath. I don`t know why Co2 is not used more often.

I guess after 30 years of fixing I have learnt a little and yes every day I hear the same old problems arising.


Comment by Kim Skinner on December 30, 2013 at 10:10am

I should clarify that no drain (zero alkalinity) acid washes can work very well for removing stains that are due to dirt, iron, and calcium scale. Pools with plaster that are over 7 to 10 years old are generally more problematic in removing stains than younger pools. 

Comment by Bruce Wettstein on February 25, 2013 at 11:42am

Thanks Kim.  In almost 20 years in this industry, I can (proudly!) say that I have never done an acid wash as I know what it does to plaster.  The no drains that we have followed have always been performed for only 2-3 days, and always on pools that are many years old and fully cured.  I am currently a fan of them-when properly done-as they do seem to produce good results (especially in pebble pools) and allow us to get in clean up the water afterwards.  That said, I only want to offer something to a customer that is beneficial, and not detrimental, to their pool, and I am always open to learning.

Comment by Kim Skinner on February 25, 2013 at 10:36am

Bruce, I am all for not wasting water.  A no-drain (acid bath) can easily be less damaging to pool plaster, including quartz and pebble, than a regular drain and acid wash, if performed properly.  The problem is when too much acid is recommended (for the no-drain) and allowed to significantly etch the surface over a week. And this applies to removing scale and/or stains on older pools. It should not go beyond a couple of days.   

New plaster finishes (including quartz) that have severe gray mottling or hardened "plaster dust" are not properly remedied by a no-drain acid bath. The pool owner may be satisifed with the improved appearance, but only because of ignorance.  The pool owner is not aware (and not told) that the surface has been compromised.  Anytime, a new plaster finish has been subjected to very aggressive conditions for a period of time, it has been etched as seen with a magnifying glass, and perhaps without.  That is not what is best for the pool.  It is etched, aged, and will begin to stain with dirt and metals much easier and sooner, and of course, will need to be replastered sooner than it would have been if not etched at the start. 

Often, the no-drain acid treatment doesn't work the first time (or at all), and the plasterer tries it again with a stronger acid solution.  I have seen pools that have been severely etched, to the tune of 36 grit sandpaper. The appearance of the pool looked better from a distance, but the pool owner's children came out of the pool with bloody feet and arms.  After that happened, the results of the acid treatment was no longer acceptable to the pool owner.

The formula for actually reducing the TA to zero is: gallonage of pool, divided by 500,000, times (X) the Total Alkalinity, equals the gallons of (31.45% strength) acid to add. 

Some might prefer to only reduce the bicarbonate/carbonate alkalinity to zero, and not include the cyanurate alkalinity.  In that case, simply subtract one-third of the CYA content from the TA and use that number instead.  Generally, that acid addition will lower the pH to 4.5, and the Saturation Index to a negative (-) 4.0.

Comment by Bruce Wettstein on February 24, 2013 at 11:35am

We follow several companies that do the no drain acid washes with our RO rig, and I have not seen anything detrimental to any of the finishes (plaster and pebble in my case) on any of the pools we've processed.  Maybe the process is somewhat different (IIRC, they drop pH to 4.0 in plaster pools and 0 in pebble pools, and keep the water highly agitated the entire time).  In the pools that have had this done that we have followed, the results have been completely acceptable to the homeowner in all cases.

I would like to see this process become more refined and a viable option to draining and refilling when pools get heavy in calcium.  We have no problem processing the water once this material is back in solution, or even if the pH is low.  We do not want to encourage plaster damage at the risk of utilizing a no drain, but we also do not like to see water waste or damage incurred from a drained pool left exposed to the air either.  If someone has a recommendation on how to do this procedure with minimal damage to any surface, I would be interested in hearing about it.

Comment by Norman Tyree on February 14, 2013 at 11:32am

Hi you fellow Genius`s  I would have thought that you would know that by putting Acid into a pool that has a Marble Based Plaster like Hydrazzo is somewhat Stupid because it dessolves the marble totally, I suggest you do a little test by getting some marble put it in a glass and add some acid and wait for it to disappear.

Kiwi Norman

Comment by Kim Skinner on February 14, 2013 at 8:59am

Kevin, Thanks for verifying the calcium increase only after a one or two day acid treatment.  

And I am glad you understand that my other comment was not directed at you. I don't think there is anything wrong with mentioning specific products, material, or equipment on this forum. In fact, it appears that some topics discuss pros and cons on specific products, and even companies.  And I agree with your last sentence.

Comment by Kevin Misley on February 14, 2013 at 7:38am

My mistake Kim in regards to promoting my product. I see the comment was not directed to me.

It is probably best for me to use generic terms for products anyway so not infer a slam or a kudo on anyone's product.

Essentially, most failures of products and materials are due to poor installation and improper procedures anyway.

Comment by Kevin Misley on February 14, 2013 at 7:32am


I looked back at my records for this job.

Calcium came in at 230 PPM before adding acid. I in fact added 3 qts of Jack's Magic Blue after adding the acid. Not 6 as I had stated previously.

I tested the water 6 hours after acid addition, the calcium level rose to 325-330. We knew the level would come but how much was uncertain. The surafce was slimy indicating it was rising.

The finish quickly began to show uniform color. The homewowner was satisfied with the color but not the feel.I re-balanced the following day.

The pool was pumped out the next day and re-polished. My plaster contractor absorbed the expense to polish and truck water in upon re-filling. The acid, Jack's, monitoring, etc.. I absorbed.

The plasterer knew he made a fatal error but we moved on for the sake of my customer and our reputations. My customer is happy and as stated refers my work.

Kim I should have clarified about the plastic. It's usually tented over not sitting directly on the surface. Yes not good right on the plaster.


I am in no way trying to promote my product. In fact it's not mine anyway. I used it as an example only. I didn't know it was taboo. I use other exposed finishes besides the one mentioned.  

Any future posts on my part I will be mindful to use generic terms if that is preferred.

Comment by Kim Skinner on February 13, 2013 at 6:29pm

Kevin, Thanks for the input. If you meant placing a tent over the pool when the rain came, yes, that would prevent the problem.  However, it would be a mistake to place a plastic tarp on the plaster surface while it is curing.  That will also result in streaky discoloration.  

I am curious about the amount calcium level increases you observed. If you recall, please provide that here, or send a private message to me.

If the plasterers that have occasional plaster issues are held responsible for their mistakes and not allowed to skate, they will quickly become informed and educated on proper practices, and will change their ways.   

Norman, it does not matter whether the mixing water is perfectly balanced for pool plaster or is low or high in calcium, TA, or pH.  The amount of calcium material dissolved in that water and plaster mix completely dominates the solution.  The Calcium level of that mix is more than 100,000 ppm. 

And please..... enough with promoting your product. 

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