DISPOSABLE MULTI-STAGE CARTRIDGE! Easy to use, disposable. Each box contains 3 cartridges. Media-grid ensures even distribution of carbon granules throughout the cartridge for maximum filtration & flow. High-strength plastic frame for increased cartridge rigidity. No-mess cartridge handle & single-piece construction keeps hands dry & clean during cartridge changes. Stage one - mechanical: Advanced multi-layered polyfiber floss traps micro & macro organic particles and foreign debris. Stage two - chemical: Super-activated carbon granules absorb many dissolved contaminants, odor, toxins, and discoloration. Stage three - biological (sold separately): High-flow bio-sponge promotes colonization of beneficial bacteria essential to a healthy aquatic environment.