Are you sure you are not fighting algae? What level of chlorine are you trying to maintain? Does it drop quickly between cycles? If it does, either your are fighting something or your CYA is low. If it doesn't, its probably something mechanical, like your cell (they do go bad) or what FBU mentioned already. Running the SWCG at 100% is going to kill it right fast, so I would be supplementing with bleach. Posting a full set of numbers might help the mods answer your questions.