Beauty; double filtration; make the water is clearer. Precisely made, smoothly buckled, and easily composed. Different sizes could be made up to fit for different fish tanks. This filter board is constructed of 3 layers, 12 pieces small filter board. Excellent material and easy to clean. Usage: clean tank and rinse thoroughly, connect the bottom plates according to the size of the tank and place it into the tank, buckle system holder on suitable plate, insert system holder from top with return system and twist to tighten, adjust return stem according to the height of the tank and lock it with a locking link. Slip a set of exhaust fitting over the return system and let air stone touch the plate. Place rinsed gravel over filter plates and fill aquarium with water. Connect air line tubing from to air switch and start pump.