DE Blowing thru

[BigDave]

... Like saying that there might be low or no CYA in a pool that eats chlorine overnight is reasonable and typical first-thing-to-check-easily response,.isn't it?

There might be low or no CYA but that has nothing to do with overnight chlorine loss.

Overnight chlorine loss is not related to CYA level but to stuff in the water being oxidized by the chlorine. A pool that loses all it's chlorine during the day might have insufficient CYA.