[Compatibility] PETSTANDARD Replacement Filter Compatible with Catit® PIXI™ Water Fountain. These are PET STANDARD branded filters and are not created or sold by Catit®. [Premium 12 Pack Pet Fountain Filters] Pack of 12 Filters [Compatible Pet Filter] Filter Measurments: 3.31" x 3.31" x 0.375" [Premium Quality Filters] Triple Filtration System: Composed of a cotton layer, activated carbon and an ion exchange resin. Effectively to filter hair, heavy metals, 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. 2 to 3 weeks in summer and 3 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!