Sand filter possibly low on sand ?

[BigDave]

The Taylor test kit is great. The advice in the book is not. Don't use the book.

[Charlie_R]

As I understand it, and I stress I could be way off base, the Taylor book does not take CYA into account with their recommendations in the book. That would, at least to me, invalidate a lot of what is in that book. A question about that, though. How can a company that makes such an excellent kit not know about something a important as that?

If you want/need to know more, Chem Geek has several posts/threads detailing the relationship, I think.

[chem geek]

See the "Chlorine/CYA Relationship" section in the thread Certified Pool Operator (CPO) training -- What is not taught for more detailed info. Even though this chlorine/CYA relationship was definitively determined in 1974 and known before then (in the 60's), virtually no one in the industry talks about it with any specificity. This is primarily due to "the big lie" from the chlorinated cyanurate manufacturers (makers/sellers of Trichlor and Dichlor) that "CYA doesn't matter; only FC matters".