I have a 28k gal gunnite pool around 12years old. I have it professionally closed but otherwise I do everything myself. I rebuilt the pump and replaced the wood in the automatic cover box this spring. My pool water is crystal clear everything is running great1 I have a cartridge filter. I have two sets of filters and change them every month. I do not have any bather complaints the PH and Alkaline are in the normal range. My problem is a cannot seem to register any chlorine. I have shocked the pool three times since may 15th with three one pound bags of super shock and have added 10gal of 15% liquid chlorine. I also keep a couple pucks in the skimmer at all times. When I first add the shock it registers on the test strip but a hour latter nothing. Anybody have any ideas. I tried a new algaecide called, "no more problems" It claims you don't need chlorine any more except the occasional shock. Thanks in advance for any recomendations.