REGULAR CARTRIDGE REPLACEMENT: Changing your paper filter cartridge is part of the routine maintenance of your pool and regular cartridge replacement can be costly. These washable and reusable foam filters will reduce your costs. SAVE YOUR MONEY AND TIME: Replacing the filter element with paper is part of daily pool maintenance. Replacing a conventional filter element can be very expensive. These washable and reusable foam filters will reduce your cost. KEEP WATER CLEAN: The filter cartridge sponge is recommended to replace one carton per week, it will keep your swimming pool, spa jet massage water pure clean and fresh, the foam filter will work for about 2 months. It applies to most massage pools, with this filter, you can enjoy the safe and healthy massage pool spa. 3 SIZES: S: pool filter length is 7.3, inner diameter: 4, outer diameter: 10.8. M: The length of the swimming pool filter is 10.2 , Inner diameter: 3 , Outer diameter: 9 . L: the length of the swimming pool filter is 20 , inner diameter: 4 , outer diameter: 10 , the filter is suitable for S type filter, which will meet your needs. WIDE USE: The filter cartridge sponge is suitable for to filter pumps using the H-type cartridge, suitable for swimming pool, spas, baths, aquariums, etc.