Aquarium Filter

A drainage and filtration system for an aquarium, comprising:

• (1) an aquarium having a drain, the drain comprising a drain opening in a bottom surface of the aquarium, the drain comprising a valve for reversibly opening the drain to allow a flow of water therethrough;
• and
• (2) an undergravel filter positioned over the drain opening, comprising:
• (a) a first housing, wherein the first housing comprises:
• a lower surface comprising one or more lower housing openings;
• an upper surface opposite the lower surface;
• one or more walls extending between the lower surface and the upper surface of the first housing;
• one or more upper housing openings in the upper surface of the first housing, the one or more walls, or both;
• and
• a compartment within the first housing, wherein the compartment is in communication with an exterior of the first housing through the upper housing openings, and wherein the compartment is in communication with the drain opening through the lower housing openings, thereby allowing a flow of water from the exterior of the first housing through the compartment to the drain when the drain opening is open;
• and
• (b) one or more pieces of biomedia material in the compartment.