The Tetra Internal Aquarium Easy Crystal 300Filter with heating compartment for crystal clear, healthy water and easy maintenance. The EasyCrystal FilterBox is a compact, space-saving complete set for optimum filtration of the aquarium water. Mechanical and carbon filtration for crystal clear water. One-touch cartridge replacement system for easy maintenance Chamber for concealing aquarium heater EasyCrystal® Filters are extremely easy to clean: replace the filter cartridge every 4 weeks. No need to rinse the filter medium, no more wet hands!