Abstract: An automatic water changing and water leveling system and apparatus is provided for use with an aquarium containing a body of water. The system comprising a water reservoir structure including a housing defining a chamber therewithin for containing fresh water. The water reservoir structure being disposed at a height above the aquarium and in approximate adjacency with an upper surface level of the aquarium water. A discharge assembly mounted to a bottom portion of the water reservoir structure is provided for discharging fresh water from the water reservoir structure into the aquarium when the upper surface level of the aquarium water falls below a predetermined level causing air to be communicated through the discharge assembly and into the chamber of the water reservoir structure allowing fresh water to be discharged. A siphoning system withdraws water from the aquarium by siphoning action thereby controlling the discharging of water from the discharge assembly.