I tested my CYA levels when I opened and was up around 90. I wanted to lower it as shocking wasn't being very effective. I ended up draining 1/3 of the pool and to my surprise I couldn't get the CYA to register on the test. I tossed some trichlor pucks in the feeder and it seems to be slowly rising, but I am at only around 20 now after a few pucks and a week of running. Anyhow is it true that you can lose most of your chlorine in a few hours with low CYA? I shocked it and the next day nothing. It's been hot and sunny for the past two weeks. I think I went through 6 pounds of shock on my small pool over the past 10 days... would you guys add more tablets and raise the feeder level or throw in trichlor grainuals at this point?