Jakebear,Originally Posted by Jakebear
These are good questions and it turns out that because CYA acts like a chlorine buffer (similar to the way that alkalinity acts like a pH buffer), the presence of CYA reduces the pH effect on chlorine's effectiveness. Of course, the presence of CYA itself significantly reduces the absolute amount of disinfecting chlorine, but once that is done it acts to somewhat keep that amount more constant when pH swings compared to not having any CYA at all. Of these two effects that CYA has -- 1) reducing chlorine's effectiveness and 2) buffering chlorine against pH changes, it turns out that the reduction of chlorine's effectiveness is huge. The bottom line is that you have absolutely no hope of restoring significant amounts of chlorine effectiveness when CYA is present by simply changing the pH.
I have to leave right now, but will add another post with some numerical examples to give you a better feel for this. It turns out that this question comes up quite a bit as people think they should run at lower pH to get greater chlorine effectiveness and don't realize that when CYA is present this inhibits their ability to do this (i.e. to lower pH to increase chlorine's effectiveness).
Richard
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