I'm trying to pick a good spot for my spa in terms of balancing the rise in pH with a too negative CSI.
Numbers (TA was 170 so I was adding acid to bring it down):
TA 40 (was over aggressive...)
Temp 84 deg F
With these numbers, I get a CSI of -0.94 from the Pool Calculator. I was going to bring up my pH via aeration, but noticed that the CSI becomes less negative as I increase my pH to 7.5 (CSI = -0.79) but starts becoming more negative as I increase pH further from there (eg: pH 7.8 has a CSI of -1.05). And at pH of 7.9, it says I entered invalid data.
I thought with increasing pH, CSI should constantly increase, but obviously I'm missing something.
My real question is even with a TA of around 60 or 70 and a pH of around 7.6-7.7 with borates, I'm still getting a relatively rapid rise in pH. If I try to lower TA to 50, the CSI gets really negative (even with pH of 7.5, say which may occur after acid addition, CSI is -0.5) which makes me worried about my plaster spa.
I'm keeping my CYA higher to slow the FC drop in the hot texas weather (lose 3-4 ppm per day, ugh).
Any suggestions on what I should do? Thanks