How do you lower high alkalinity when the pH is low without going in circles?

Question

I have an in-ground fiberglass swimming pool and, due to my own error, the alkalinity is very high - think around 200. My pH, however, is quite low. I've been going in circles with muriatic acid (lowering alkalinity) and soda ash (raising pH). I know these are working against each other, but I'm stumped as to how else to fix this. We're not getting great suggestions from our pool store. I would really appreciate any suggestions. I feel like I'm wasting quite a bit of time and money the way I'm doing things now.

Answer 1

To lower TA, you add acid to the deep end of the pool, away from any return jets. It sinks to the bottom ( have your main drain suction turned off, if you have one) and changes ONLY your TA. It leaves the pH alone. It's called slugging. You need to adjust the TA first, before pH. In your situation, with the elevated TA, you have what's called pH lock. That pH isn't going to budge no matter what you throw at it until your TA comes back into range.

Once you've dropped your TA, the pH may even come back up on it's own, since many chemicals ( chlorine included) have a high pH of their own, which will raise it in the pool water. Give it a day or so after you've brought the TA down, to see if the pH will come back by itself. If not, adding pH increaser in front of a pool return in the shallow end will do it. The soda ash you're using by the way...is going to mess a bit with your pH. Try Borax instead ( sodium tetraborate). It's a pH increaser as well but tends to leave the TA more or less alone, compared to soda ash. A little goes a long way as well. Use it sparingly.