Highly active biological filter sponge in sizes - specially developed for the Tetra EX 1200 Plus and EX 1500 Plus aquarium external filters Suitable for an aquarium size of up to 600 liters Provides a large surface area for beneficial bacteria to colonize, removing harmful substances such as ammonium and nitrite Tetra BF biological filter sponge reliably removes medium-sized particles from the aquarium water Rinse in lukewarm water before use