Includes 8 carbon filters and 8 foam filters. Replacement filters measure 7.6 x 4.2 cm; the sponge has an inner diameter of 6 cm. Please measure your filter housing before ordering. High quality material: The cat fountain filter has a cotton surface that contains coconut shell activated carbon, and a sponge to protect the pump. The outer layer of high-density cotton isolates the water from impurities such as hair, effectively purifying the water for cats. Easy to use: The cat fountain filter is easy to install with the raised side up and the flat side down. Both filters provide adequate filtration and help eliminate odors in the fountain. Maintenance and replacement: To prevent activated carbon dust from settling in the water, soak the filter in water for 5 minutes and rinse thoroughly under running water before first use. Replace the activated carbon filter every 2 to 4 weeks, depending on how often the fountain is used and how many pets drink from it. Replace the sponge filter every two months. Use scenarios: - Multi-cat households or fountains with high turnover benefit from continuous filtration and odor control. - Homes with long-haired cats where hair and impurities tend to accumulate in the water are improved by the cotton outer layer. - Between deep cleanings, these filters help maintain water quality and protect the pump for reliable operation.