Is pH 8.7 acceptable if csi is zero?

Update: Over the winter, the pool water never got below 34F but there was a chance it might so I winterized and closed. However since the water never froze I continued checking the pH and chlorine every few days and adjusting when needed. I mixed the water when I added chemicals (mostly acid) by dropping 2 high flow submersible pumps in the pool at opposite corners (One pump was 8000gph and the other was 5000 gph). I left the pumps in about 30 minutes to get a good mix then pulled them out.

The pH kept rising with no end in sight all winter until suddenly it stopped rising about 12 days ago. That might not seem like a lot of time but I had never gone more than 2 or 3 days max without the pH going well over 8 since my pool was installed May 2023.

The pH was 7.5 12 days ago and its only 7.8 today. (My pH meter is calibrated regularly and is a bench top ampera700 and is very accurate.)

My fingers are crossed that my pool plaster has finished curing and that i will no longer have to frequently keep adding acid every couple of days.
 
I think your TA 50 is the reason for your stable pH.
Based on my research I would agree except that during my frequent acid additions in the past I had adjusted the TA down to 50ppm for several months but it did not slow down my persistent pH rising….my pool has been covered since December with a solid cover with a 5’x3’ mesh in the center and the PH stopped rising on its own about 4 or 5 days before I uncovered it. Water temperature is fluctuating between 62 and 67F depending if it’s sunny outside.
 
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