Cleans gravel quickly and easily. Easy to install and operate:Should gravel become lodged in impeller, remove the bases of the unit by gently pulling down. Then remove gravel. Use two size "C" batteries(not included), avoid any electrical shock. Just press the power button to start, place the cleaner as the position you desire to clean fish excrete and other dirt in the aquarium. It can be used to change aquarium water. With flexible structure, its length can be extended. Suitable for small and large aquarium.