Quote Originally Posted by CarlD View Post
You have other factors acting to raise pH. Many people have a constant rising pH with SWCGs (I don't--don't know why). Many people also have rising pH while their masonry pool is curing. So all your tri-chlor was doing was offsetting some of the upward pressure on pH.

I went away once for 2 weeks (9 or 10 years ago) and left 4 floaters full of Trichlor tabs. When I came back, my CYA went from 30 to 70, my FC was about 5 or 6, but my pH had dropped below the measurable bottom of 6.8. 4 boxes of Borax later I was back in the 7's. At the time, here, there wasn't much discussion of the acidity of Tri-chlor tabs, merely of the additional stabilizer. So I asked the question and the answer came back: Tri-chlor is highly acidic.

The SWCG on balance is actually a pH neutral process. Initially, during the production of chlorine from salt, the chemical reactions raise the pH. But eventually, when that chlorine oxidizes organics or kills algae, those processes are inherently acidic. So on balance an SWCG pool should see no pH change. @chemgeek has some very extensive posts on the chemistry of the SWCG process.

But yes, trichlor is acidic and I have both borates and other factors that suppress the pH drop from that. I was just commenting because pH dropping from trichlor is not inherently an issue for me and I should be more cognizant to warn others about its acidity.

Wow, that's a crazy pH drop though!!