I replastered my pool a month ago, and the plaster is looking good. We're going into the winter season, however... and the water is quite cold, about 50 degrees. I live far enough south to not have to close the pool entirely, and would use the spa every now and then.
My fill water has high TA and low CH, so I added a little CH to bring it to 200 two weeks after the replaster, and added acid in regular doses to bring the TA down while keeping the pH in range.
So, now today, my results are (using trichlor pucks to add CYA over time until I get it to 30-ish):
FC = 5.0
CC = 0.0
CYA = 20
pH = 7.7
TA = 140
CH = 190
No salts no borates. With these plugged into the CSI formula, I get a CSI of near 0. Or -0.03 to be exact. Just where I want it to be.
But my question is: as my TA drops further to the 70-90 range, my CSI will go down into negative territory. To balance that, should I add more calcium hardness? Or should I allow my pH to rise to 7.8-7.9? I'm afraid to add more calcium hardness because of potential scaling. What would you pool gurus do?