[Compatibility] PET STANDARD Replacement Filter Compatible with Kastty® 101oz/3L Water Fountain. These are PET STANDARD branded filters and are not created or sold by Kastty. [Premium 12 Pack Pet Fountain Filters] Pack of 12 Filters + 12 Pre-Filter Sponges [Compatible Pet Filter] Filter Measurments: Outside Diameter 5 inch. Thickness is about 0.4 inch. Pre-Filter: 2" x 1" x 0.5" [Premium Quality Filters] Double Filtration System: Composed of a cotton layer and activated carbon. Effectively to filter hair, keeps water fresh and improve the taste of the water. [Frequency Of Replacement] To prevent the activated carbon dust from shedding into water, please soak the cat fountain filter in water for 2 minutes then rinse thoroughly under running water before using. 1 to 2 weeks in summer and 2 to 4 weeks in winter. If multiple cats are using the fountain, more frequent replacement will be necessary. [Friendly Customer Service] Please feel free to contact us if you have any questions about our products, we'd like to help you!