BIO-Wheel Power Filters deliver simple, easy, 3-stage aquarium filtration...without the hassle of air pumps, valves, tubing or air stones.Now there are new features, new sizes, increased flow rates and a BIO-Wheel thats up to 50% larger! The new two-piece filter hood provides quick flip-top filter cartridge access. A noise- reducing vented cover ensures quieter operation. The adjustable mid-level intake increases water circulation throughout the aquarium and the larger 200 and 350 models feature extra media slots -- you can add an extra Rite-Size Filter Cartridge or Penguin Refillable Media Cartridge for enhanced chemical filtration. Convenient Penguin Rite-Size Filter Cartridges come ready to use with each filter...ready to mechanically and chemically remove waste, discoloration and odors. Each contains new faster-acting Black Diamond Premium Activated Carbon for maximum efficiency. Biological filtration is provided by the revolutionary BIO-Wheel - proven best at removing toxic ammonia and nitrite. Maintenance is fast and easy. The Rite-Size Cartridge changes in seconds - with no messy assembly required. And the BIO-Wheel never needs replacing! Info from United Pet Group