Water loss due to evaporation won't bring your CYA down--it just concentrates the CYA in the remaining water in the pool until you refill, then the refill just dilutes it back to the same level it was before the evaporation. If you're wanting to bring the CYA down, it'll have to be done by water actually removed from the pool--splashout, backwashing, draining to waste, etc.

Janet