Inert ceramic material with open flow architecture and largest use-able surface area. Higher efficiency relative to conventional media results requirements to achieve treat NH4-N and NO3-N. Most technically advanced bio-filtration substrate. The surface of the block is a microporous and has a large specific surface area. It is suitable for the growth of various microorganisms and forms a stable and highly active biofilm on its surface. The three-dimensional void (3D) formed by the sphere and the sphere produces a powerful bactericidal effect. They are a great base for sponge growth, micro-fauna, and even coral frags. Bio-Filter Block will work in sumps, trickle filters, wet/dry filters, hang on the back filters or directly in the tank. Suitable for use in fresh, marine and pond water! Size for 1 block: 10cm x 10cm x 2.5cm