Biochemical FiltrationThis fish tank filter has 1 box with biochemical cotton inside, can collect and filter the waste in water, make wave and circular flow, help to culture beneficial bacteria, create a healthy water environment for your fishes and turtles. The biochemical cotton is washable and reusable. Increase OxygenThe air inlet on the aquarium filter will increase oxygen level of the filtered water, make the fish more active. Also, a good supply of oxygen helps culture beneficial bacteria like nitrifying bacteria. You can adjust the oxygen supply by spinning the valve of air inlet. P.S.: The valve of the oxygen inlet should be placed outside the fish tank and contact with air. Ultra QuietPremium pump motor is noiseless during operation. It is only 35 dB, almost like the whisper or the sound in a quiet library. We recommend to turn off the spin button and stop the air inlet process at night, so that the filter pump will be more quiet. This way, it will not affect the operation of the filtration. Easy to CleanIt is very convenient to take out the biochemical cotton and wash it, or your can replace with other filter medium. If you have any questions about our products, please feel free to contact us