You may have heard aquarists talking about their "Biological Filter", but do you really know what it is? The answer may surprise you. The larger your biological filter is, the more fish your tank can safely hold. You probably have more biological filtration in your tank than you know.
More: Choosing Your Biological Filter Material Which materials are more efficient?
More: Nitrifying Bacteria Tank Starters can help get your aquarium's biological filter started.