When you test in the evenings, add enough bleach to take the chlorine level back up to 10ppm. If you find that by the next evening when you test again, that you have dropped below 5ppm, take it up to 12 instead. You want to take the chlorine level up high enough so that you never drop below 5ppm. I'd start out by testing every night but after a while, with a CYA of 80-90, you may find that you are able to test and add bleach every other night. But, don't start out that way. And, make sure you stay above 5ppm at all times or else you risk an algae bloom.