Bio Balls are plastic spheres designed to greatly increase the surface area present in a wet/dry type of filter. The sponge inside increased surface area creates a much larger area for beneficial nitrifying bacteria to grow on, consequently increasing the amount of biological waste that the filter is able to process effectively. Bio Balls also increase the oxygen level in your tank and encourage gas exchange in your filter. Thanks to their pronged design and smooth surface, Bio Balls do not easily clog with organic matter, and are inert. Perfect for both biological filters and gas exchange reactors and are safe for both freshwater and saltwater aquariums. As an added bonus, bio balls help quiet the sound of falling water that typically accompanies wet/dry filter systems.