Optimised bio-filter medium with perfect volume utilisation, long service life and maximum degradation performance. Substrat pro consists of spherically sintered quartz. The spherical shape allows a high bulk density. In this way, the volume in the filter (filter baskets or modules) can be fully utilised. In addition, the optimized surface of the beads ensures intensive colonization of the important cleaning bacteria. A dense bacterial lawn is formed. Due to the high number of bacteria, nitrite load peaks are also better reduced and the service life of the filter material is extended. Eheim Substrat pro is suitable for fresh and sea water, is washable and can be used several times. Biological filter material. The main task of the biological filter material is to provide the best conditions for bacterial cultures to settle, so that a bacterial lawn is created after a short time. The bacteria feed on dirt particles of all kinds and convert the substances critical for the aquarium. After the first cleaning by mechanical filter masses (e.g. Eheim Mech or Mech pro) the biological filtration is the most important thing. It ensures clear, healthy water and stable water values. Therefore, we have invested a lot of research work in the development of biological filter media.