High Density Foam Sponge for cats and pets, compatible with replacement filters for 2.5L cat fountains. Please check the size of the sponge filters in your fountain before purchasing. - Pre-filter action: removes hair, dirt and food residue before water reaches the pump, protecting the fountain pump and extending its life. - Additional protection: captures impurities and dirt. The included ion-exchange resin filters the water again, helping each drop be cleaner and fresher and helping prolong pump life. - Compatibility and size: designed for 2.5L cat fountains; verify fit for your model before buying. - How to use and care: soak the filter in water for 2 minutes, then rinse thoroughly under running water before use. - Recommended replacement intervals: 1 to 2 weeks in summer, 2 to 4 weeks in winter. If several cats use the fountain, replace more frequently. Use scenarios - Routine maintenance for a 2.5L cat fountain to protect the pump and keep water clean. - Multi-cat households where higher hair and debris buildup occurs, requiring more frequent changes. - New installations or ongoing use where maintaining water quality and pump longevity is a priority.