Use of Tetratec Aquarium Filter Replacement Foam BF800/1000 in Tetratec Internal Filters IN800 & IN1000 ensures that the aquarium water is filtered effectively. Biologically active bacterial cultures that transform harmful nitrite into the plant fertiliser nitrate settle in the filter foam. The foam structure also carries out physical filtration, removing visible particles from the aquarium filter. Also suitable for use in marine water aquariums.