Wide Compatibility: Our fountain filter fits most 1.6-2.5 liter cat fountains! Cut : 125*125 mm, inner diameter 35 mm. More Efficient: The filter comes with activated carbon, which can help remove chlorine, odors and contaminants, effectively filtering out dirt, thus providing cats with fresh water. With this filter, you can encourage your dogs and cats to drink more and promote pet health and hygiene. Note For Use: Please rinse the filter with water and make sure the filter is thoroughly wet before installation. Keep flat side up to install. 2-3 Week Change: We suggest changing the filter every 2-3 weeks to ensure the best protective filtration for our pets. Tips: Make sure the filter size fits your fountain before purchasing; and clean the filter thoroughly with water before using.