The advanced Tetra BF Biological filter foam is designed to be used with the Tetra external filters EX 400, EX 600 and EX 700. The highly advanced biological foam provides a large surface area for the growth of beneficial bacteria. These bacteria removes harmful substances e.g. ammonia and nitrite from the aquarium water. The foam also mechanically removes medium sized particles from the water. Content: 2 pcs.Do you have questions about this article ?