What is a 'BIO-wheel' for an aquarium?

What is a 'BIO-wheel' for an aquarium?

Marc Grover (Professional Aquarist) gives expert video advice on: Generally, how do filters work in an aquarium?; What are the best filters for a small freshwater aquarium?; What are the best filters for a large aquarium? and more...

A BIO-wheel is a modern version of a biological filter. It works like a wet dry but it's really compact. It's a small wheel that has a lot of pleats in it, and it's typically on one of the hang on waterfall filters. The water gets sucked up through the tube and goes to the filter stages, and then as the water is falling back out of the tank it strikes this BIO-wheel. The BIO-wheel is not totally submerged. It's spinning through the waterfall. If you can imagine a barrel with fins on it spinning in a waterfall, part of the time it's submerged but most of the time it's in the air. It's a wet dry filter, and bacteria need oxygen so all that air is hitting all the bacteria and it's working like a under gravel. It doesn't have the surface area that an under gravel does, so it's not quite as efficient, but it is a combination filter where you have got the water for mechanical aspect and the BIO-wheel biological aspect.