Abstract: Self-contained aquarium system having a tank with a bottom wall and side walls for containing water. A filter unit is disposed in the tank and provides a filter surface which is spaced above the bottom wall of the tank. A dividing wall is provided within the tank and forms a main compartment and an equipment compartment in the tank. The dividing wall has an opening therein to permit the flow of water from below the filter grid in the tank and into the equipment compartment. A removable enclosed filter box is disposed in the equipment compartment and has an opening therein in registration with the opening in the dividing wall and has another opening remote from the first named opening. Filter material is disposed in the filter box and is arranged so that water entering the first named opening in the filter box and leaving through the other opening will pass through the filter material.