Shop Swimming Pool Stores for Pool Cartridge Filters- the filter of choice for most spas, and many smaller above ground pools. The cartridge filter is enjoying a resurgence in popularity. The cartridge filter element, an aquatic version of the pleated air filter in your car, traps dirt and particles of 25 - 100 microns in size. The cartridge is removed from the tank and hosed thoroughly, top to bottom, with a high pressure hose to remove dirt when the pressure gauge rises 8 - 10 lbs. above its clean reading.