Advanced Aquarium Filters
Published: Tue, 23 Sep 2008
By: Michael Oleksak
Power filters
Most people agree that power filters are much easier to maintain and can be as economical as undergravel filters. There are many styles of power filters, but the most common hangs on the back of the tank. A siphon tube pulls water from the tank into the filter box and passes the water though a mechanical filter (typically a porous foam sponge). The sponge doubles as a biological filter. A internal pump then returns the filtered water into the aquarium. These power filters come in many sizes suited for small to large aquariums.
The foam sponge can be easily inspected for clogging or removed for cleaning. You must clean the sponge regularly to remove the solid wastes before they decompose and dissolve back into the water. It is quite important that when you clean the porous foam that you do not kill the bacteria colony through the use of detergents, very hot or very cold water. A safe and easy way is to rinse the foam sponge in the bucket into which you have just drained some tank water during your regular water change routine.
Power filters now come with all sorts of fancy features. Most allow placement of a chemical filtering media, typically granular activated carbon, in the water path.
Another development in the last few years is the wet-dry wheel (called a biowheel by one manufacturer). The beneficial bacterial colonies that neutralize toxic ammonia require an oxygen rich environment to grow. The wet-dry wheel passes water over a water wheel device which sits outside (on the edge) of the aquarium. This rotating wheel maximizes available oxygen allowing a large bacteria colony to flourish.
One drawback is that these wheels have been known to jam, so you need to check them frequently. Other than this minor point, the wet-dry wheel is an excellent method of providing vigorous biological filtration.
The Canister filter
Canister filters have some similarities with the hang on tank style of power filters, but the essential difference is that canister filters are designed to provide more powerful mechanical filtration.
Typically, the water is pumped, at moderate pressure through a filter material, such as glass wool, or a micron filter cartridge. Canister filters are especially useful in aquaria with large or numerous messy eaters that generate a lot of waste. For these filters to be effective they must be frequently cleaned, to avoid the decomposition of waste in the water stream.
These filters usually sit on the floor below the tank, but also can hang on the tank, and in some designs even sit inside the tank, in which case they are called a submersible filter.
Some hobbyists attach a wet-dry wheel to the outflow of their canister to improve the biological filtration capacity of this type of filtration system.
Wet/Dry Filters
Also known as trickle filters, wet/dry filters work on the principle that the beneficial colonies of ammonia neutralizing bacteria grow best in the presence of well oxygenated water.
By trickling water over unsubmerged plastic gizmos or other media, wet/dry filters provide a very large air/water surface area. They come in many shapes and sizes. The boom in successful saltwater aquariums in the 1980s can be attributed to the use of this filter type.
Many things can used for the media, with the best providing great amounts of surface area, while at the same time having large openings to reduce the tendency to clog and ensure efficient gas exchange. The problem of clogging of the media can also be reduced by prefiltering the water with an efficient mechanical filter, and (when used) with a protein skimmer.
Protein skimmers (aka Foam Fractionators)
Protein skimmers were initially developed for use in industrial sewage treatment plants where they are also known by the term foam fractionator. Protein skimmers have the unique ability to remove dissolved organic wastes before they decompose!
This is a neat trick which is accomplished by taking advantage of the fact that organic chemicals are attracted to the surfaces of bubbles which are passed in large numbers through a column of water. The foam is then skimmed off the water, while at the same time removing the organic wastes. The foaming process only works in a water with high pH and salinity, and as a result skimmers are primarily for saltwater use.
The protein skimmer is largely responsible for the boom in reef aquaria in the 1990s, due to the high water quality possible with this type of filtration. A current state of the art in reef systems is based upon the use of protein skimmers and live rock without the use of a wet/dry filter. This school of thought is known as the Berlin method.
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