TFP likes CSI, which, if I remember correctly, is a derivative of LSI. LSI was originally developed for some other industrial purpose, CSI was the modification for use with pools. I probably mangled some of that, but it's close.
There is a CSI calculator in the Pool Math app. Or you can use the original version. It's a webpage, and the link is at the bottom of every TFP website page, named "
Old PoolMath Webpage."
The webpage requires you fill in all your pool's levels. The calculator in the Pool Math app uses your current or latest test result entries, which makes it very convenient.
I used the webpage for my calculation above, but I use the Pool Math calculator each time I run a suite of tests. I monitor CSI weekly. As the annual conditions change, especially pool water temperature, I use the calculator to adjust my pH. As the water cools, I have to allow my pH to rise, in order to keep my CSI between -0.3 and 0. During the summer, I drop my pH to keep my CSI as close to -0.3 as possible. -0.3 is best for SWGs, as that slightly lower number keeps the SWG's internal plates free of calcium deposits. If you don't have an SWG, then 0 is the target, but anything between -0.3 to 0.3 is fine.
While TA, CH, CYA and Salt levels are all used in the CSI calculation, it is water temp and pH that affect CSI the most. Since I have no control over water temp, I use pH to counter the effects the water temp has on my CSI. They are inversely proportional. The higher the water temp, the lower the pH, and vice versa. FC doesn't affect CSI.
It's very much simpler than it sounds, especially using the Pool Math app. You'll find that if you're maintaining all your levels within TFP ranges, the CSI will also be within TFP's CSI range. EZPZ.