A bit confused

[chem geek]

Bob,

I'm not sure what you mean by "even where the TA is at this time" since your TA is definitely too high. You can most definitely aerate. As far as how frequently to check pH, I can't tell you that because it really depends on how effective your aeration is. Just test it after a few hours and if it's not changing very much you can check on it less frequently, but when it goes up measurably (say, from 7.2 to 7.4) you can add acid to bring it back down. I assume you may have an acid demand test to tell you how much acid to add, but I can give you a rough idea BUT it depends on your TA level so as the TA gets lowered it will take less and less acid to bring the pH back down from 7.4 to 7.2. If your pH test reliably tests down to 6.8, then you can use 7.0 as your target or 7.1 which would be in between the 7.0 and 7.2 colors on your test. The point is that this process is more effective at lower pH, but don't worry that being right near 7.0 is going to somehow destroy your vinyl -- it won't. You just don't want it to get much below 7.0, that's all, so using 7.0 or 7.1 as your "target" during this process is fine.

As an example for your 9600 gallon pool, when the TA is at 250 ppm it takes 26 ounces or 3 cups 2 ounces of Muriatic Acid to go from a pH of 7.4 to 7.2 (43 ounces or 5 cups 3 ounces to go from a pH of 7.4 to 7.1).

For comparison, at a TA of 150 ppm it takes 16 ounces or 2 cups to go from a pH of 7.4 to 7.2 (27 ounces or 3 cups 3 ounces to go from a pH of 7.4 to 7.1).

For technical reasons it takes less acid to lower the pH in a higher pH range than in a lower pH range, so trying to get to a much lower pH gets progressively harder -- kind of like pulling on a spring. That's why the amount of acid to get to 7.1 compared to 7.2 seems to be more than one might expect.

Richard