I have a bit of a mess on my hands right now. Did the pool drain to get the CYA down... I got a ways to go. Got my chem test kit and still unsure if I'm getting it right. My estimation is ~ 100 but it might be wishful thinking or my power of focus on that dam dot. So took to the pool store to see if they get the same. They got 134, which is about the same they got on 3/27. OK, more draining needed in either case. But when I took my TA value I got 120ppm. They adjusted my TA value to 75 because of the CYA level. I'm afraid to ask, but what's the math behind that?