Are you testing your CYA with strips? Even the two best--Hache and LaMotte are pretty worthless on that test--you cannot tell if your CYA is 0 or 50! I know, I've used them. I MAINLY use them to check if my chlorine is there or not, but I look at the others and try to figure them out. Frankly, the ONLY way to measure CYA is with the black-dot test tube.