Okay that answers that, Thanks. I'm finding myself in a block situation where I can't keep chlorine in the pool. Shock at night, nothing in the pool the next day. Found you guys while looking for answers. My pool was a green mess when I opened last month. Got it looking sparkling, everything seemed fine then all of a sudden no chlorine. Shocked a couple times but not getting anywhere. I need some test results, so will try to get the Leslie FAS-DPD kit tonight so I can see where the CYA is at and I can get started. PH keeps dropping so I turned of the chlorinator, because someone on here said that would happen if I was using 3" pucks. I will be in touch tonight if I can get the kit. If they don't have one, maybe I will get a water test just to get an idea where i am at.