Internal filter for aquariums. Air enters the vertical tube through a smaller side tube which is powered by an air pump and draws the aquarium water upwards, returning it to the aquarium after first passing through a fine-pore sponge with an ideal surface and being mechanically cleaned. Nitrifying bacteria, essential for the biological breakdown of pollutants, settle inside the sponges. It is ideal for the breeding of larvae and fry or young fish, which under other conditions would disappear into regular filters due to their small size and limited swimming ability.