Rising Ph?

[court475]

I've been putting muriactic acid in my pool almost daily to get my TA down, which started with fill water at 370. It's now down to 200. My Ph never seems to go down much with the acid though. I ran out and didn't add any for 2 days, and it went from 7.2 to 7.8. Is it normal for acid to rise so quickly? Might I really need to be adding acid every day, and how safe is that?

Thanks!

[chem geek]

Yes, when your TA is that high this means your pool is way out of equilibrium with the amount of carbon dioxide in the air. In a sense, your pool and fill water are overly-carbonated and the outgassing of carbon dioxide will cause your pH to rise. This will continue until either your pH goes way, way up or, after adding acid, your TA goes way, way down. However, as you approach a TA of 100 or 80, then you will find it easier to maintain a pH of 7.5 with little or no rise in pH nor addition of acid. The following table (http://richardfalk.home.comcast.net/pool/CO2.htm) gives you some sense for how low you will have to go since you are way, way in the "red" zone with significant outgassing of carbon dioxide (off the chart with high TA -- I just updated this chart with higher TA values -- you probably need to get just to the "green" region).

You should follow Ben's guide to lowering alkalinity (http://www.poolforum.com/pf2/showthread.php?t=191) and aggressively get your TA down. This will indeed require a lot of acid, but once it's done, you will have very little pH rise nor acid demand.

Having fill water with such a high TA will make things difficult for you even when you get your pool TA lowered. Because you will be adding water to your pool to make up for evaporation, splash-out, and possibly backwashing of your filter, this means that you will always have to do some lowering of TA periodically, but it won't be nearly as bad as now since you'll only have to bring down the TA by a much smaller amount (essentially, just for your fill water).

One thing you might consider is to put your fill water into a smaller basin or tub exposed to the air and ideally aerated (stirred or splashed, etc.) and leave it like that for several days before putting the water into your pool. You can add some acid to this water to aid in this process, but follow Ben's procedure (albeit on a much smaller scale) to not lower the pH too much. Then, you will be essentially adding the proper TA water to your pool each time and won't have to deal with trying to lower your entire pool's volume of water.

Richard

[court475]

Thank you so much, Richard! I get it. :)