Carbon Block Cartridge for removing chlorine before reaching the RO membrane. Coralife Pure-Flo II Thin Film Composite (TFC) Reverse Osmosis Water Purification Systems generate purified water for aquarium use. The units remove hardness, heavy metals, toxins and many other tap water impurities. The Coralife Pure-Flo II units include clear filter canisters, cartridges and faucet attachments. The Pure-Flo II units are economical, convenient and wall-mountable. The Coralife Pure-Flo II units are usable with chlorinated and well-water sources. Great for Freshwater or Saltwater Aquariums. Works with Pure-Flo II units - 76000, 76001, 76002, 76003, and 76004