# Marine Aquariums > Saltwater Beginner's >  What Is A Biological Filter

## lost

The biological filter in an aquarium is nothing more than a place for bacteria to grow. Any surface in an aquarium which comes in contact with the nitrosoma bacteria that you created when you cycled the tank is part of your biological filter. 

The type of substrate you choose for your tank makes a great difference in the amount of surface area that is available for bacteria to reside on. Choosing Your Biological Filter Material is important when setting up your filtration system.

The efficiency (strength) of a biological filter is determined by its surface area. Some filter medium are more efficient than others. Aquarium glass surface area aside, here are the most popular biological filtration methods:
Canister Style Filters come in many different styles and sizes and can also be multifunctional.Live Rock / Berlin Systems are the filters of choice for many SW aquarium purists.Live Sand  Systems are also very popular with many reef aquarists.Undergravel Filters are among the first biological filters created for SW aquarium hobbyists.Wet / Dry Trickle Filters were the next step after the UGF to dramatically improve efficiency.Biological Filtration Polls show you which biological filters are popular with other hobbyists.Knowing how each biological filter works and what it requires will make Choosing a Filtration System much easier.

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