The Catit PIXI Fountain Cartridge is a 3-stage filtration with filter pad that removes magnesium and calcium from tap water. Use this great product to assure that the water your cat drinks is clean and healthy at all times. Key Features: Cotton mesh filters out debris Active carbon removes odours and impurities Ion exchange resin softens tap water Rinse filter with running water to clear away excess carbon dust. Place Filter into designated area of fountain with foam side facing up. Replace filter every 30 days.