I'm in my second season with the liquidator,works good. I dont have it in front of me but I think the manual says to add when one or two inches from the bottom. You can shut off pump and let the liquidator dran down for adding chlorine or hold float valve up so no water enters to add. Someone suggested adding a shut off valve to stop water flow, that's a good idea that I havent got around to doing yet,but it sounds like the best way. Either way it's no problem to add chlorine.