EHEIM SUBSTRATpro Bio-Filter Media (250 ml) is a high-performance biological filter medium made of sintered glass beads that provide an enormous surface area for beneficial bacteria colonization. The spherical shape and porous structure allow for very dense bacterial growth, enabling efficient breakdown of ammonia and nitrite for crystal-clear, healthy water. Suitable for freshwater or marine aquariums, SUBSTRATpro is pH-neutral and long-lasting – it can be rinsed and reused multiple times without losing effectiveness. By incorporating SUBSTRATpro in your filter, you create stable biological conditions and extend the interval between filter cleanings, since its optimized design supports an above-average bacteria load for reliable filtration.