The present invention provides amultifunctional submersible pump, which provides multiple functional selections suitable for various types of aquariums, including water circulation and filtering, pumping out wastewater, oxygenation, and carbon dioxide refining. The bottom portion of the submersible pump is provided with a water inlet, a water outlet, a wastewater drain outlet, and an adjustment knob. Left and right rotation of the adjustment knobenables water circulation and filtering or pumping out wastewater, as well as enabling adjusting the amount of water flow. One side of the top portion of the submersible pump is fitted with a retainer ring, which enables disposing an aquarium lamp therein. Another function of the present invention lies in the design of the simple assembly method of the CO2 refiner, whereby the refiner can be easily disassembled for cleaning when a ceramic refining disk placed inside the refiner is obstructed by pollutants.
