How to Choose a Filtration System for an Aquarium

Understand the three types of filtering systems you'll need in your tank: mechanical, chemical and biological.

Consider the different kinds of filters and the needs they address. Wet-dry filters (also known as trickle filters) are best for saltwater tanks, because they provide mechanical, chemical and biological filtration. They're fairly expensive but require less maintenance than many other types.

Remove impurities from the water with a mechanical filter. It's designed to move water through filter floss, filtering particles from the water.

Keep in mind that chemical filtration uses media such as activated charcoal to remove wastes that have dissolved in the water. The charcoal traps particles that cause bad smells and yellowing of the water.

Establish your biological filter before you add fish to the tank. Biological filters use bacteria to break ammonia and nitrites down into nitrates. If you add too many fish too soon, the bacteria can't keep up and the ammonia levels in the tank will rise, killing your fish.

Buy an aquarium kit and you'll get an undergravel filter with it. This cheap biological filter pulls oxygen - rich water down through the gravel and then pumps it up through lift tubes. Bacteria grow on the gravel, so you should have at least 2 inches of gravel on top of the filter. Because a lot of waste gets sucked through the gravel, it requires frequent cleaning with a gravel vacuum.

You might notice a clear, plastic box sitting in the corner of some tanks. This is a corner filter. Air is lifted through a tube with bubbles, through a bed of filter floss. Bacteria grow on the floss, providing excellent biological filtration. These filters are unsightly, require more maintenance, and take up space. But they're cheap.

Opt for sponge filters. They are another efficient and cheap biological filter. Water is forced through porous foam, either by a powerhead or bubbling on air through a tube.

Take the easy way out. Power filters are easier to maintain and can be as economical as undergravel filters. The most common style hangs on the back of the tank. A siphon draws water from the tank into the filter box and through a mechanical filter - typically a foam sponge, which acts as a biological filter. An internal pump returns the filtered water.

Go for a similar version of the power filter. Canister filters work somewhat like the power filter. Water is pumped through a material such as glass wool or a micron filter cartridge, providing mechanical and chemical filtration. Depending on the model, these filters can either sit on the floor behind the tank, hang on the tank, or go inside of the tank (called submersible filters).