fountain filter replacement designed for most fountains with a square water pumps and oval or rectangular filter slots Simple installation: place the black sponge over the pumps intakes and secure the white pad in filter slot Pet fountain filter replacement for optimal and water freshness, we recommend a simple routine: refill with freshly water and clean the fountain every 2-3 days, and replace this filter combo every 3-4 weeks The main pad traps hair and debris, softens water, and reduces scale-causing minerals Before first use, rinse under water until wet to activate the media and remove any carbon It ' s then ready for immediate use