Before Order - The fountain filter's is 7.6*4.3cm (due to manual measurement, there is an error of 0.1-0.3mm). The inner diameter of the sponge is 6cm,Please measure the size of the filter housing before ordering. Safety - The filter is composed of non-woven fabric, activated carbon and natural resin, which can effectively isolate impurities such as hair in the water, improve the water quality and protect pets' safety . Sponge is used to isolate impurities in water from entering the pump, to allow the drinking fountain to operate safely. Use - It is pretty easy to replace the filter from cat fountain. In order for the work better, please soak the carbon filter thoroughly before use. Regular - Please replace the filter regularly (once every 4 weeks for Carbon filter , once every 2 months for Sponge foam). If the temperature is hot and humid, increase the frequency of replacement, to avoid breeding of mosquitoes. Survice - For any questions, suggestion or complaint, please contact us d.