Filter foam for EasyCrystal Filter 250 and EasyCrystal FilterBox 300 with intensive biological filtration for crystal clear, healthy water. This filter foam is designed for the EasyCrystal Filter 250 and EasyCrystal FilterBox 300. It provides intensive biological filtration to ensure crystal clear and healthy water for your aquarium. The cartridge replacement system allows for easy maintenance. Contents include 1 foam filter.