I have a Doheny's Pool Pro Deluxe Cartridge Filter, 150 sq ft System with 1 HP Pump and notice this season I have to clean the filer at least once a month to keep the water moving through the pump. I have two cartridges that I swap out instead of running the same one all the time. The filter cartridge isn't really that dirty when I clean them, it appears the pressure in from the return diminishes after 24 hours. Putting in a fresh cartridge restores the pressure through the return but 24 hours later its back to barely moving water. Just dont think the cartridge's gets that dirty in 24 hours. Any suggestions?