Looking at Power Filters for Your Saltwater Aquarium

A power filter is the one of the easier and least complicated water-filter systems for your saltwater aquarium. The design is simple: Water is pulled into the filter media and pumped back to the tank. You can choose from external, external with a biowheel, or internal (submersible) versions:

• External power filter: This unit looks like a big square cup that hangs on the outside of the tank, and it's powered by its own motor. The filter generally contains filter floss or filter sponges and activated carbon as the filter media. Water is drawn into the filter by a U-shaped intake tube, flows through the filter media, and is pumped back to the tank either through a tube or a spillway. The filter media provide mechanical and chemical filtration; biological filtration is established as the filter matures, and bacteria colonize it. Therefore, these filters provide all three kinds of filtration and are specifically designed to turn over large amounts of water. The power filter also circulates the water, providing valuable aeration.

These filters are easy to maintain — most have simple cartridges that can be routinely replaced. Remember to retain half of the used filter floss or use a sponge-type media so that you can hang onto helpful bacteria.

• External power filter with a biowheel: The biowheel rotates so that it comes into contact with both the air and water in the filter. As water moves through the filter, the wheel spins, exposing millions of bacteria that live on the wheel to the air and the water. Because these bacteria need air to efficiently convert ammonia, this system provides enhanced biological filtration in your power filter. Biowheels don't need cleaning, so they enable you to retain these bacteria even if you replace the internal filter media.

Biowheels are also offered as separate units that hang on the back of your aquarium and are powered by a powerhead or canister filter.

• Internal power filter: Also known as submersible filters, these are similar to external versions, but it sits inside the tank. That position takes up valuable tank space and obstructs the view. Some newer models, however, are neatly disguised as aquarium decorations. Most models provide mechanical, chemical, and biological filtration.

Internal power filters are smaller than external versions, so they hold much less filter media. As a result, they process less waste from the water, and you'll need to clean them more often.

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