The blue filter sponges for the BioTec ScreenMatic² 40000 flow-through filter are easy to use and very easy to clean. They are components of the biological/mechanical filtration in the BioTec filter: Coarse dirt particles are retained in the coarse-pored blue bio-bodies. Due to the enrichment with oxygen, Nitrosomonas bacteria quickly form in the blue zone, which convert ammonia, which is highly harmful to fish, into nitrite. Also suitable for the predecessor model BioTec ScreenMatic 12. Contents: 2 filter sponges