Bio Sponge is the best filter material for your koi pond for decomposing organic material. Other filters are able to clean up waste and feces but cannot remove other organic matter such as mucous membranes, koi urine, zooplankton carcass, phytoplankton and other microscopic organisms, as well as protein from food. Only bacteria can remove it. With Bio Sponge, this waste, these excrement and this organic material are filtered.