The answer to your question is a function of both CYA and FC (total free chlorine) levels since twice the chlorine level loses about twice the amount of chlorine per day. I now have around 15 CYA and 2-3 ppm FC and lose about 0.5 ppm per day. The pool is normally covered and is open to sunlight (it's an outdoor pool) about 14 hours per week. I used to have more CYA, but had more chlorine and the rate of loss was about the same.