trying a non aggressive no drain acid wash

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SUNOFTHEBEACH

SUNOFTHEBEACH

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May 20, 2008
108
Waldorf, MD
Opened my pool in early may to calcium scale that trapped dirt under it. At one point the entire bottom of the floor and all of my steps were stained. Recently I lowered my PH to 7.2 and held it there for a week. I am making progress and I believe if I held my PH to low normal for the entire season, the pool would be clear. I am not that patient and want a clean pool sooner.

last night I added acid and brought the PH down to 6.9.

1. At 6.9 PH, am I at the point where I shouldn't run my pump?
2. Am I at the point where I should remove my stainless steel light ring and light assembly?

I have tons of, I assume calcium dust. I feel like my DE filter is not keeping it in the filter.

3. How do I remove the calcium dust?

I have read the Zero Alkalinity acid wash post. The Zero Alkalinity Acid Treatment

I have read the article 20 times and I do not know if it advocates doing a Zero Alkalinity treatment or not. It seems to be bashing the Zero Alkalinity treatment.

The gist of the article is add enough acid to get your Alkalinity to zero and keep it that was for 7 days. It will eat away 8 pounds of plaster and you pool will be clean, but it will be etched and cause you issues in the future. They surmise that 4 gallons in a 20,000-gallon pool with a starting TA of 100 will drop your alkalinity to 0 and your PH will be 4.5. Again I dont know if this article advicates for the procedure or not.

4. Is the Zero Alkalinity treatment a guideline or is it a sarcastic article bashing the procedure.

5. Has anyone successfully done a Zero Alkalinity treatment?

Here is a current pic. At one point all of the steps were covered in the stain. Keeping my PH an low normal has probably cleared 60% of the stain. The stains showed up darker in the pic then in real life.

 
It's hard to advise you when you have no pool details in your signature. But some general comments -

1. You should never do a zero alkalinity treatment without the ability to by-pass your heater (if you have one) as the low pH can damage the internals.

2. It is best to not circulate your water once the pH drops below 6.5 and to just use your wall brush for mixing. This avoids getting low pH water in the pump and filter housing (and protects SWGs).

3. Any cloudiness or calcium dust can be removed later once you have neutralized the acid and brought the TA back up to normal

4. All lights and metal object should be removed form the pool water to avoid corrosion

5. After the zero alkalinity treatment has been allowed to progress, your water will now have higher calcium levels due to the dissolved plaster. If excess scale was also removed, then one should consider draining some of the water and replacing it with fresh water or else the CH will be higher after the treatment and put you right back into danger of scaling again.

6. When raising the pH back up, you should ONLY USE baking soda to raise the TA and then brush the pool vigorously to aerate the water. This will cause natural pH rise and calcium can not form scale with bicarbonates.

As for the article, the point the expert there is trying to get across to the reader is that ALL FORMS of acid washing are "methods of last resort" as they do damage to your plaster. All forms of acid washing remove a layer of plaster from the pool and what is mostly etched is the calcium carbonate part of the plaster matrix (plaster is a mixture of calcium carbonate and calcium silicate and calcium silicate does not dissolve in acidic water conditions). So any acid washing treatment is going to leave your plaster MORE porous than the original finish which can lead to a greater affinity for staining or developing algae.

So YOU AND ONLY YOU can decide if the risks of doing a zero alkalinity treatment is worth the potential reward of a cleaner pool surface. There is no absolute standard here as every pool is different and every pool owner accepts a certain degree of risk according to what they can tolerate. What the experts who wrote that article will tell you is that an ounce of prevention (keeping your pool water chemically balanced and clean) is worth far more than a pound of cure (trying all sorts of chemical potions to fix a problem).

Good luck and post back if the process works for you.
 
You should carefully watch your pool and perhaps take before/after photos or create a test spot of some kind to monitor the process. You are etching your plaster and it can easily go too far. I would say you should stop as soon as those stains disappear and not wait some arbitrary length of time like 7 days.

We had one very bad incident reported here where the pool builder used way too much acid and the pool owner just followed the PBs advice and let the pool sit at low pH for over a week. By the time the pool owner realized something was wrong, the plaster was etched down beyond its aggregate and the surface was horribly rough. Luckily the PB admitted his mistake and paid for the re plastering of the pool.

Good luck.
 
My PH is creeping back up. It dipped to 3.9 yesterday morning and it is at 5.0 today. I assume a PH of 5 is ok for a no drain acid wash.

I am getting scared though. It is very hard to find anyone on the interwebs that say they have successfully done a no drain acid wash.

Almost no one on this Forum has done it!

Local Pool store gave me a quote of $650 for a drain, acid wash, then power wash service.
 
As calcium carbonate dissolves from the pool wall back into solution, the carbonate anion (CO3^2-) is not stable at low pH and converts to bicarbonate and then dissolved CO2. In the process, it consumes two protons (H+) and that raises your pH. So what you're seeing is the effect of carbonate ions in pool water.

Keep the pH low and make sure the TA remains zero during the process. When the stains are lightened or gone to your satisfaction, quench the acidity with baking soda to restore pH balance. You may want to dump some water in the process to remove excess CH.
 
I wanted to close out this thread in case someone searches for the no drain acid wash. I don't think it works in anything except mild cases. I don't think you can get the PH in 20,000 gallons of pool water low enough to etch and clean the pool. I think the time on contact is tool long to be reasonable.

It is very hard to find someone on the internet that claims to have done it successfully.

while my pool clearly got better, it would have never gotten drain and acid wash clean.
 
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