Replacement cartridge for the sediment pre-filter of the Rhino EQ-300 Whole House Water Filter System. Sediment pre-filter cartridges should be replaced every 3-4 months. The sediment pre-filter is used to prevent dirt and sediment particles from entering and clogging the main filter unit. Each pre-filter cartridge should be replaced every 3-4 months depending on water quality and sediment levels. For best results, change the cartridge when water color darkens or water flow slows.