How do you test Ph if the Cl' levels are 25ppm? CYA level is around 100 maybe a little higher. Raised Cl' up to 25 - 30 ppm to shock the algae. Ph was a little low before we started adding the 12.5% Cl. I did add borax before we added the Cl' to get it close to 7.2 range. Ran out of Borax.

I retested the CYA level with 50% pool water and 50% well water. Came up with 100 so that is about 200. I am not sure what level the CYA level is now.

This mornings numbers:

TA - 40
FC - 32 ppm
CC - 0
Ph - off scale low
CYA - ~200

I tested water again 6 hours later and FC levels have not changed. Originally I thought the CYA level was 100, that is why we tried to start to treat the water.

How much water needs to be drained and refilled to lower the CYA?

I came up with about 20,000 gallon pool with vinyl liner. 17' by 32' in-ground 3 foot shallow end to 8 foot deep end.