I am new to pool keeping and have a major algae problem right now. I have been reading the forums and have been shocking the pool for the last 2 days with liquid shock. The water is starting to clear, but I am having some major problems with the cartridge. I have a 21' ABP with a 1HP pump and a 75 sq ft cartridge filter. The problem is the cartridge. After running for about 3 hours, the cartridge is completely green and the water does not filter at all. The pool store recommends using bacquacil (sp) to soak the cartridge. We have done that without that much success. We purchased a new cartridge and it was in the same condition as the old one within 6 hours. Is there something we can do to get the algae completely off the cartridge or to prevent ruining another new one? At $50 a pop, we can't afford to keep replacing the cartridges, but we know we can't get rid of the algae without good filtering.