sera internal filter L Air operated sponge filter These air operated internal filters work as a mammoth or airlift pump. It is pushed into the standpipe via a hose by an air pump. The air draws aquarium water upwards with it in there, water flows back through the fine mesh sponge that provides an ideal surface, and thus purifies the aquarium water mechanically. The nitrifying bacteria important for pollutant breakdown settle inside the optimized sponges. These filters are ideal for rearing larvae and juvenile fish that otherwise would disappear in normal filters due to their small size and swimming behavior.