Set of 2 Catit Dual Action Fountain Filters for use with the Catit Stainless Steel Drinking Fountain (50023). This premium quality filter collects large particles and debris, helps reduce odors and absorbs impurities. The Dual Action filters are of Catit certified quality and are guaranteed to safely and optimally purify your cat's drinking water for approximately 30 days. After 30 days, filtration effects will start to gradually decrease and bacteria may start to form within the fountain reservoir. Replace your Catit Dual Action Filter every month, or sooner, if the filter is visibly saturated.