Abstract: An elongated air discharge tube extends along the bottom of a chamber in an elongated housing. The housing is placed on the bottom of an aquarium tank along a side wall thereof. The tube includes a plurality of upwardly directed air discharge openings. The discharged air flows upwardly through the chamber and then through openings in the chamber's lid, to issue as a wall of air bubbles into the tank. The rising air bubbles create a circulation pattern of the water in the tank, first upwardly with the air curtain, then laterally across the tank to the opposite wall thereof, then downwardly, then back along the bottom of the tank to the air curtain side of the tank. The inlet to the air pump chamber may include a filter chamber in which a replaceable filter material is provided, for mechanically removing suspended particles from the circulating water.