New finish - high Ph

[tigerpilot]

Naples Florida. Inground pool 9,000 gallons, Salt system. New finish is Florida Stucco exposed aggregate. CYA 80. Salt 3500, Temp 80.
I'm finding that I have to add about a quart of acid every few days to keep the Ph down to normal levels. TA is about 150. Hardness is low but someone suggested that I don't try to correct the hardness 'cause the new finish will elevate it somewhat. No problems with chlorine level. Is adding that much acid normal and if so, how long before it sort of normalizes?
Appreciate any help.
Regards...

[chem geek]

Yes this is normal for any sort of new plaster-like finish. The pH will tend to rise rather quickly so a lot of acid needs to be added regularly and the Calcium Hardness (CH) will also rise over time.

The curing of concrete produces calcium hydroxide where a 5 ppm CH rise results in around a 0.4 pH rise (at typical starting pH and TA levels).

The tendency for the pH to rise will occur for months, but this drops off fairly rapidly especially after the first weeks and after a few months the rise will be a lot less and you'll need a lot less acid. Usually after a year, the surface is very stable and you won't see any excess pH rise from that though you could still see the pH rise from other sources such as aeration of the water especially if the TA is too high.

HOWEVER, an SWG pool tends to rise in pH anyway and your TA level is far too high. It should be more like 80 ppm as the high TA will tend to outgas carbon dioxide faster. (Read the link below on plaster start-up -- if your builder is doing a bicarbonate startup, then the TA will be higher in the first month). You could also consider adding Borates to your pool as an additional pH buffer either from Proteam Supreme Plus or other similar pH balanced borates product or from a combination (added separately) of 20 Mule Team Borax and Muriatic Acid. The Borates won't change the amount of acid you need to add, especially during curing, but it will slow down the rate of pH rise so that perhaps you can add the acid less frequently. However, check with your pool builder as he may not want you to add borates until after the first month.

You can read more about a new plaster startup here and about water balance for SWG pools here.

Richard

[Guest]

And the risks of lowering ph or TA too much with a plaster pool starts erosion of the plaster especially when the surface is still new and soft.

[Pooltech32]

I personally would get my Calcium up to about 150ppm, it will rise a little bit but not that much and you want to protect your plaster.