1. The set includes: you will receive 8 pieces of carbon filters and 8 pieces of foam filters. The replacement filters measure 7.6 x 4.2 cm, and the sponge has an inner diameter of 6 cm. Please measure the size of the filter housing before ordering. 2. Quality MaterialThe cat fountain filter features a cotton surface infused with coconut shell activated carbon, along with a sponge to protect the pump. The outer layer of density cotton effectively isolates impurities like hair from the water, providing pure water for your cat. 3. Easy ApplicationThe cat fountain filter is simple to use—just install it with the raised side up and the flat side down. Both filters ensure thorough filtration and eliminate odors for your pet. 4. RecommendationTo prevent activated carbon dust (nontoxic to pets) from settling in the water, soak the filter for 5 minutes and rinse thoroughly under running water before use. the activated carbon filter every 2 to 4 weeks, depending on usage and the number of pets using the fountain. the sponge filter every two months.