Hello, I have a 15k gallon in ground pebble tec pool with AutoPilot SWG, Polaris cleaner, and Sta Rite filter system. Over the last month or so, I've been having problems keeping up my chlorine levels without adding additional chlorine manually. I cleaned the salt cell which helped a little, but still can't keep chlorine. I am attempting to SLAM the pool now. I superchlorinated to 24ppm last night and was down to 18ppm this morning (lost 6ppm overnight). Before I added the chlorine, I sprayed off the filter cartridges. I don't have any visible algae although I did have a small amount of yellow algae and the pink algae/bacteria stuff earlier in the season. My CYA level is at 50ppm. A test for ammonia showed 0.5ppm. What are some other causes of chlorine loss? Should I just continue the SLAM until I'm not losing chlorine over night?