How much water do you have to drain, natural splashout, or evaporation before you see a change in levels such as CYA or CH or any other levesl that may be affected. I usually do not drain any as it is so hot here it will evaporate soon enough. My levels are fine, but about a month ago I tested and got a CYA around 40 and tested last night and got 30 doing it 2-3 times in a row. Also my CH dropped from 350-325. Nothing to worry about, but just wondering how much water loss you have before those change.