Removes organic film and dust from the water surface Delivers oxygen rich surface water to the filter which enhances the growth of nitrifying bacteria A special skimmer valve also allows water intake from the middle and bottom of the aquarium Provides complete water circulation and filtration For freshwater or marine aquariums Includes 2 BIO 3 Filter Cartridges Filters 125 gph and is rated for tanks up to 25 gallons.