The innovative EasyCrystal Filter Pack C 250 300 is suitable for both EasyCrystal Filter 250 and EasyCrystal FilterBox 300 filters for your aquarium. With its intensive physical, biological and chemical filtration, the filter cartridge ensures crystal clear, healthy water. For best results, change the filter cartridge every four weeks. No need to rinse the filter medium, meaning no more wet hands. Tetratec Easy Crystal Filter Packs are a complete filtration media which uses physical filtration with double layer filter floss pads that reliably remove even the smallest of particles from the aquarium water.