With that CYA, you can't let your chlorine get below 8ppm. Search for one of mwsmith2's posts and download his bleachcalc program if you have a PC. Otherwise, you can estimate that one gallon of bleach will add approximately its percentage concentration in ppm to 10,000 gallons of water. In English, 1 gallon of standard 5.25% bleach will raise 10,000 gallons of water by 5.25ppm