I think I can get my SI in the middle of the range and feel good about it. However, that is using a current pool temp of 84. The SI drops alot when you lower the pool temp to, say, 50 degrees. I am planning to shut down my pool for the winter, so I won't be running the pump and I won't have the opportunity to alter the pool chemistry. What happens to my plaster pool when the temp drops and the SI falls out of the safe range for potentially 2-3 months? This has me concerned.
I guess there is a difference between the standard Saturation Index (Si = pH + Ti + Ci + Ai - 12.1) and the Calcite Saturation Index found at the Pool Calculator? I'm getting significantly different results, so I just wanted to check.
I'm also a bit confused that the Pool Calc's CSI gives me a 0.01 even though my pH and TA are considered high at 7.8 and 130 (CH=172, CYA=61, temp=84, salt=3200, borate=0). Lowering pH and TA to 7.6 and 100 results in a CSI of -0.32 at 84 degrees, which puts me in the danger zone if/when the temps fall into the 40's or lower.