PH after Acid wash

[markphin]

Hi All,
I had my pool re tiled and new coping. Upon completion the contractor acid washed the pool. All is filled with new water and looks like a new pool. My understanding is the acid washing opens up the pores of the plaster and causes your PH to push up for a period of time. My question is how long will it take to get PH back to normal. Its been about 3 days so far and have been adding about half a gallon of muratic acid per day to 30,000 gallons of water.

Thanks in Advance.

[CarlD]

I'm not the expert here but I understand that curing takes up to 6 weeks. If your CYA/stabilizer is low, it's an ideal time to use Tri-Chlor tablets as they are VERY acidic.

[markphin]

Thanks for the quick reply Carl. I understand the six weeks for new plaster, but is that the case for existing plaster too as all I did was an acid wash? I'm hoping not six weeks as I'd like to close in 2-3.

[CarlD]

I can't offer any better advice...I am not a masonry pool expert.

[markphin]

Thanks Carl. Hopefully someone else will chime in.

[SunnyOptimism]

Thanks Carl. Hopefully someone else will chime in.

I wanted to chime in but was not able to when I first saw this post. Indeed, fresh plaster surfaces can take a long time to cure as the slack lime (Calcium hydroxide) in the cement converts to calcium carbonate through hydration and CO2 absorption. That is why the pH rises, the plaster surface is literally sucking CO2 out of the water. This is also why some also strenuously argue for the "acid-start" process as they say the low pH drives more CO2 out of solution (assuming your carbonate alkalinity is high enough).

For cured plaster that has just been acid washed, the loss of CO2 to the fresh plaster surface should be minimal as it should have already converted to calcium carbonate. I suppose there could be some slack lime left in the old plaster but I would highly doubt it.

If you're still experiencing large pH variation, I would suggest doing a full suite of water testing as the pH swings may be due to water which not properly balanced.