I know CYA can be lost to splash-out and drain-off, but does it -ever- go away all by itself just due to environmental conditions?

The reason I ask is that I'd like to run my pool low on CYA (20ppm or so) and just barely crack open my auto-chlor with the 3" trichlor pucks inside while using bleach for most of the chlorine.

I now know how much CYA each puck is adding, but I don't know how much is going away by itself, if any.

Thanks,

TW