Quote Originally Posted by PBLsQuad450 View Post
I'm not sure why bleach doesn't drive up the ph more?
The short answer that explains this seeming conundrum is that though the pH does rise when you add bleach (or any other hypohchlorite source of chlorine such as chlorinating liquid, Cal-Hypo, or lithium hypochlorite), the pH falls back down again when the chlorine gets used up -- that is, when the Free Chlorine (FC) drops back down. This is because the consumption/usage of chlorine is an acidic process that balances out the initial rise in pH from the chlorine addition. I explain this technically in this post, but that's chemistry that will probably cause you nightmares so avert your eyes if you accidentally click on the link.

The only net pH rise will be from the "excess lye" that is added to bleach and chlorinating liquid (and less so with Cal-Hypo), but this amount is low in high quality bleach products like 6% Clorox Regular unscented which has a pH of 11.9 and in high-quality chlorinating liquid that has a pH of 12.5. There are many off-brand 6% Ultra bleach products that have more excess lye in them and have a pH of 12.5, 13 or more and would tend to have the pH rise more quickly.

There is also a tendency for pH to rise in pools due to carbon dioxide outgassing, but this can be minimized by keeping the TA lower. Finally, the pH can rise substantially in newly plastered pools due to the curing of plaster.

Richard