Today I was sent to a pool that had turned cloudy when one of our techs added pH increaser (Sodium Carbonate). The pool is an 18x36 rectangle (about 24,000 gal.), vinyl liner, with a SWG.
My initial assumption was that the Calcium Hardness was probably too high, and when the pH came up, the water precipitated CaCO3. I tested the water with a TF-100, and I'm kind of surprised with what I found, and confused as to why it turned cloudy. This pool has had some issues this season. It was struggling to maintain chlorine levels, and cloudy every other week for the first half of the season. I hit the pool hard with chlorine, and stayed on it for about 4 days. (Not quite a SLAM by definition, but the best I can do given the circumstances) From that point on the pool has been stable, and has had no problem maintaining adequate FC levels. The tech that regularly takes care of this pool has had problems every time he adds pH increaser with clouding. I've experienced similar rapid clouding in other pools, but typically it dissipates within a day or so.
This time the pool clouded completely, and there was a renter at the house, so they called and complained, and I was sent out to see what I could do. Here is what I found:
I talked to the tech about the chemistry he observed the day before, and the only differences would have been in pH and TA. He said the pH was down around 7.0 so he added 4lb of pH increaser.
When I punch these numbers into the PoolCalculator, I see that the CSI goes from negative to positive with this change in pH, but it doesn't seem to push it far enough to justify the instant clouding of the entire pool.