Biopellets are based on the principle of immobilization. Waste products from the water, mainly nitrate and phosphate, are converted into bacteria thus keeping the aquarium water cleaner. Biopellets are composed of biologically degradable polymers that can be placed in a fluidized filter or filter canister. Biopellets will allow aerobic growth of bacteria which consequently will consume nitrate and phosphate simultaneously. The bacteria will use up the carbon from the BioPellets, whilst nitrogen and phosphorus are taken from the water as nitrate and (ortho)phosphate. This conversion of organic BioPellets (together with inorganic nitrogen and phosphorus) into microbial biomass is called immobilization. In addition, anaerobic layers will develop, resulting in additional denitrification. Surplus bacteria will be consumed by filter and suspension feeding organisms such as sponges and corals, or skimmed off by a protein skimmer.