Hey John, welcome to the forum!!

The only scenario which I can think of right away is interference from another test. Let me explain what I mean - the 44 ml side is used for pH/ TA and CH, if you do the pH after doing Alk or CH without completely rinsing the chamber, some of the other reagents may be present in sufficient quantity to lower the pH reading. I'll assume that subsequent (higher) tests are done without having run the other tests - therefore an accurate reading. I imagine that if you're dumping the test water back into the pool where you are taking the samples that similar interference could occur. That's the best theory I could come up with in 5 min. Perhaps someone else has an alternate theory (Waterbear may well have better insight into this)

While I don't know much about pebblsheen, I believe the pH rise only occurs when the material is curing - perhaps it's fully cured.


Again, welcome to the forum - Waste