Math/New Water Help

[chem geek]

As you point out, usually the pH slowly rises when using bleach or chlorinating liquid. Usually, the pH only drops when using Trichlor or Dichlor or when using non-chlorine shock (MPS). It will also drop when chlorine goes from a high FC to a lower FC. The pH will drop some going from colder water temperature to warmer water temperature -- going from 45F to 80F would drop the pH from 7.5 to 7.2 (with your TA and CYA levels).

Usually with the higher TA such as you have, the pH will tend to rise if the pool is uncovered (or has a mesh cover) so can outgas. Unless your CH is high, I wouldn't worry about your high TA right now until we sort out the pH drop. You'll want a higher TA to help compensate for that if we can't otherwise figure out why the pH is dropping.

It's possible that the new liner has some sort of reactive chemical on or part of it and this is leading to greater chlorine demand. It's possible that this chemical might also be acidic leading to a lower pH when getting into the water. However, I've never seen anyone report this situation before and it seems odd.

Richard