Abstract: An upwardly opening aquarium tank is provided including an outwardly convex partial spherical bottom wall. A base is provided including a standard portion of large cross sectional area defining an upwardly opening pressure chamber and the standard portion includes peripheral wall structure from whose upper marginal portion the bottom wall of the tank is supported. Seal structure is provided for forming a fluid tight seal between the tank bottom wall and the standard portion and the bottom wall includes air inlet check valve structure opening therethrough by which pressurized air from the pressure chamber may be admitted into the interior of the lower portion of the tank through the bottom wall thereof. The base includes an air pump for supplying air under pressure to the pressure chamber and a light diffusing filter panel is supported from the valve structure and overlies the bottom wall in spaced relation relative thereto.