We have some disagreements here-- I've found that with a vinyl pool, personaly, 150 is OK for T/A but others insist 100 is the max. I'm not saying they are wrong, but I haven't had the problems they say can develop...I may have just been lucky.

However, I don't like pH at 7.8 and suggest lowering it to 7.0...then aerate (splashing kids playing are good) to raise the pH back over 7.2. This will lower your T/A as well, killing 2 birds with one stone.

Are you using cal-hypo to chlorinate or shock? That stuff CAN push pH up.

Falling CYA is due to dilution unless you have a NASTY algae bloom.