Quote Originally Posted by chem geek View Post
Well, the flaw in that calculation is that colder water would have CYA degrade far more slowly so then you are left only with the water dilution as an explanation and that only partially accounts for the CYA drop you see.
You didn't mention water temperature. I wonder if having a foot of ice has any effect. Can Isocyanuric Acid be frozen without breaking down? My winter pool usually has a foot or more of ice in January/February.