Cartridge filters these filters use a pleated paper or non-woven fabric to filter out debris, they can have many cartridges or just one. Those that use only one cartridge fits over generally have a center shaft that the cartridge fits over. If there are many cartridges, they fit on a manifold. Because the filter needs to be taken apart to be cleaned, they can be more labor intensive. Typically the cartridge elements must be removed for cleaning, hosed off, soaked in a filter cleaning product, hosed off and put back into the filter housing. Having to allow the element to soak 8-24 hours, you need a minimum of two cartridges or two sets of cartridges. They should be replaced every one to two seasons for maximum filter efficiency.