My pool loves low TA

[chem geek]

Carl,

That's the whole counter-intuitive thing about TA. While higher TA would normally have less of a pH swing with a given acid/base introduction, this apparently is not the case when the source of rising pH is primiarly due to carbon dioxide outgassing which occurs at a faster rate at higher TA. These two factors compete against each other, but the outgassing wins out so that there is actually LESS pH rise AND LESS acid demand at lower TA. This is what BillyBumbler is experiencing and is what many others have experienced as well. This thread at post #31 shows the lowering total acid demand AND rate of rise in pH when KurtV lowered his TA to 60. This thread also talks about rising pH and how lowering TA reduced both the rise in pH and the acid demand but this was not that apparent going from 120 to 80. In this thread the lowering of TA to 80 did result in slower pH rise and less acid demand.

So my conclusion is that lowering the TA mostly works at reducing the rise in pH and the amount of acid needed to restore pH. This is, no doubt about it, one of the most counter-intuitive things in all of pool water chemistry, but it does seem to be true -- at least when the primary source of pH rise is due to carbon dioxide outgassing. The pool store advice of increasing TA to reduce pH fluctuations simply doesn't work and actually makes the problem worse when the pH rise is due to the outgassing. Not only will higher TA result in somewhat faster rising of pH, but the acid demand grows even faster.

Richard