Corner or Box Filters
Filtering Your Aquarium Water
(The First Tank Guide)
What Is a Corner Filter?
Corner filters are any filters where the water is drawn through filter media in a plastic or acrylic box, which sits inside the tank. Most of the time these filters are made of plastic and are powered by an external air pump.
The box itself will have holes in the top and bottom or front and back, depending on the way that water is moved. The box itself can be opened to accept a variety of filter media, however, usually these filters will use filter floss or batting and a small amount of activated filter carbon.
How Does a Corner Filter Work?
A corner filter uses bubbles of air from an external air pump or an integral water pump to draw water out of the filter box. As water is drawn out through the holes in the top or back of the filter, it is replaced by water that comes in through the holes in the bottom or front of the filter. This action pulls the water through the filter media. The floss in the filter will provide mechanical filtration and the carbon in the filter will provide chemical filtration. Both the carbon and the floss, as well as the sides of the container will provide a bed for the bacteria of a biological filter. Most corner filters primarily provide mechanical filtration.
What Maintenance Does a Corner Filter Require?
You will have to regularly change the media in your corner filter. The amount of carbon that can be used in most corner filters provide viable chemical filtration for 1 to 4 weeks, depending on tank load, tank size, what other filtration is available, cleaning schedule, and whether or not any chemicals, additives, plant foods, or medications have been used in the tank. Remember to remove any carbon from the tank or filter before you medicate (if the carbon is working, it should remove the medication from the tank in under an hour, in which case your fish won't get treated).
The floss or sponge(s) will need to be rinsed or replaced every time it becomes dirty. As with the carbon, this will need to be done every 1 to 4 weeks, depending on tank load, kind of fish, feeding schedule, type of food, cleaning schedule, and what other filtration is available.
What Should I Be Aware Of with a Corner Filter?
Most corner filters are reasonably efficient filters, but corner filters require a lot of maintenance, and the regular maintenance of the filter requires the replacement of the filter media. If you have a corner filter, you should consider getting a second filter so that you do not remove all of your bacteria bed every time you clean the filter. Removal of the biological filter media (and its bacteria bed) will cause your tank to cycle again, which can be fatal to your fish.
Usually, the biggest issue with corner filters is that they are often used in small tanks and bowls, where you can least afford to be losing water volume and space to an internal filter.