[Installation Method: First always remove the sponge before filling with water. Second Add water until the water level is close to the filter outlet. Last power on the filter wait for it to function properly then insert the sponge. (NOTE: Inserting the sponges first will block the outlet of the water pump causing slow water intake and loud noise.) Multiple Filtration: With 2 bio sponges for double filtration the aquarium hang on filter effectively traps debris or wastes and accumulates nitrate. Provide mechanical and biological filtration to fully remove harmful substances. Oil Film Removal: The telescopic oil film skimmer can automatically float to the water surface and rotate 360° continuously with water flow. Greatly absorb oil film on the water surface keeping your fish tank crystal clear aerated and healthy. Compact & Quiet: Featuring a compact and delicate body the fish tank HOB filter is hardly noticeable when hung on the tank wall. Perfect for nano aquariums up to 5 gallons! With noise less than 30 dB it’s extremely quiet and causes no disturbance at all. Adjustable Water Flow: Come with a rotatable knob on the water inlet. You can freely adjust water flow rate as needed. A small waterfall from the filter outlet keeps the water circulating greatly increasing oxygen solubility and enlivening the aquatic lives.]