Fluval BIOMAX U2/U3/U4 Filter Media. Fluval BioMax provides an optimal environment for the colonization and growth of beneficial bacteria. The unique bio rings have a complex pore system that provides an optimal environment where beneficial bacteria can thrive. Fluval BioMax also reduces and controls ammonia and nitrate. Key Features : Provides an optimal environment for the colonization and growth of beneficial bacteria Unique bio rings have a complex pore system that provides an optimal environment where beneficial bacteria can thrive Also reduces and controls ammonia and nitrate Perfect for freshwater and marine environments Designed for Fluval U2, U3, U4 Underwater Filters 170 grams (6 oz)