Filter cartridge for Tetra Easy Crystal FilterBox 600 ensures crystal clear, healthy water thanks to its intensive mechanical, biological and chemical filtration Mechanical and biological filtration: the double-layer filter fleece with a large surface area reliably removes even the smallest suspended particles. White side = coarse pre-filter; soft, beige side = fine filter. Quick, clean change: no washing out of the filter medium, no wet hands. With Timestrip: indicates when the filter cartridge should be changed.