The two most common ways of filtering aquarium water are by either Mechanical or Biological means, and quite often a combination of these two both together. Don't worry if this sounds all too techie , by the time you get to the end of this article you will quite comfortable with these terms. The most common way to filter the water in the aquarium is to draw it out of the tank by means of a tube, then allow this water to pass over different materials like cloth, plastic balls, sand or charcoal (these are referred to as Mediums or Media ). The filtered water is then returned by way of tubes or spill gate back to the aquarium. The second way to filter water in the aquarium is biological, and that simply means to have a biological reaction within the gravel or substrate as it is referred to, to filter the water. Water is sucked from the tank, through a medium, like gravel, and microbes/enzymes that live in the gravel break down the impurities in the water.

There are many different types, brands, models of filters and filter accessories; I will cover the basic types of filters in this article, these being the ones most commonly found in use in today's aquariums. Filtration comes in a wide range of shapes, styles and processes. May people break down filtration into groups like Bacterial filters and Mechanical filters. To make this series of articles easier to read, as well as being designed for the first timer, I am just going to break down filters into two easily defined sub groups, Internal and External filters.

Internal filters are those filters that are primarily housed within the aquarium itself, and may rely on an external power source such as electricity or air pressure.

External filters as you probably already guessed are like internal filters, but moved outside of the aquarium.

Why some many different kinds of filters? Well every one wants to design a better mousetrap, hence we have ever more confusing styles, types brands and models to choose from. These include, but are not limited to the following:

SPONGE FILTER:

A sponge filter is basically a pad of sponge with a tube rising out of the center of it. Generally an airline is hooked to the sponge filter: The air is delivered from an air pump to the bottom of the filter, then the air travels up this tube (referred to as a Lift Tube ). As the air travels up the tube, it draws water along with it. This pressure created is what is known as a venturi effect, just like your grandmother's old percolator coffeepot. Air moves upwards, taking water with it, the water moving up is drawn from the bottom of the tank. The water flows through the sponge onto the lift tube. The sponge traps and collects the debris in the tank. Microorganisms living on the sponge helping to break down the chemicals in the tank like Ammonia and Nitrites into less harmful Nitrates. How did ammonia get there? Well, it is produced from fish waste byproducts (urine and fecal matter) and leftover food particles. For more information on this, look forward to next issue's article in which I will cover the chemicals in the water that are commonly referred to as the Dreaded Cycle and also talk about testing the different water qualities.

CORNER/SUBMERGED FILTERS:

Although this is submerged in the tank, it acts like the first type of filtration that was briefly discussed above. It is normally powered by an outside air source or a small internal electric motor. Air is introduced through the bottom of the filter, drawing water with it through the filter by creating a vacuum. The water passes over cloth and charcoal then returns to the tank through an outlet normally located towards the top. Both Corner and Sponge filters do not have a lot of flow through them, so they are ideal for small tanks; especially tanks with fry (babies) in them. These type filters are very inexpensive and require biweekly cleanings at least. Additional necessary costs include an air pump and air hose. The Corner Filter also requires activated charcoal or other material and cotton batting/filter floss, available in stores.

UNDER GRAVEL FILTERS (UGF'S):

This Under Gravel Filter (or UGF, as they are referred to) is the most common filter found in today's aquariums. The UGF is the second type of filtration that we discussed earlier in the page. As you can see in the graphic, there is a slotted plate, a covering of gravel or substrate and lift tubes. These lift tubes either have an air stone and line inserted into them, the rising bubbles cause the water to circulate, just like in the Corner or Sponge filters. Or the tubes have what is known as a power head attached to it. A power head is an electrical submerged pump that provides high water flow for larger tanks. This type filter is probably the easiest for the experienced hobbyist to maintain and the most difficult for the beginner. It requires patience when first starting out, something most beginning hobbyists do not have. The UGF draws the water down from the tank, through the gravel where the fish waste material gets trapped and broken down by enzymes. The water flows under the gravel in a cavity that the plates have provided, up the tubes and is introduced into the tank. If a power head is used a great current flows into the tank - the direction and rate of flow can usually be directed. Additional costs include gravel, air pump or power head (most likely a combination of both) lift tube filter caps (this is the black area you see at the top of the tube) and charcoal or another material depending on what the water conditions require. Since I have recently had so many e-mails concerning the actual set up of this type of filter system, look for an article on step by step set up coming soon.

BACKPACK FILTERS:

This is the second and probably most commonly found filter in aquariums under 50 gallons in size. An electric pump draws water up and out of the tank via a slotted tube powers the backpack filter. The water goes into a large well and passes through a cartridge of cottony material and charcoal, sometimes a sponge as well. Then the water drops over the spill gate and returns to the top of the tank. The flow rate on some models can be changed for lighter duty during feeding times, and when you have very small fish that may be sucked up into the filter. For very neat and tidy filters (biweekly maintenance) simply remove one filter and replace with another. This is more costly but involves fewer hassles than any other filter system. Some of these types of filters have Bio-Wheels ; these are rotating drums of pocketed material. The pockets allow for a bacterial growth that aids in killing off the bad waste in the water. This is very low maintenance, and I encourage their use. Additional costs are cartridges and the occasional impeller or tube when one breaks.

CANISTER FILTERS:

The canister type of filtration is the least visible and most expensive type of filtration. Some canisters also allow the hobbyist to decide what type of filter medium and how much of it he/she wants to use. Other canisters have pre-manufactured filters and medium packs that you can purchase individually or in larger more economical packs. I really like the simplicity behind the canister filters; I also appreciate the fact that they are the least intrusive to the aquarium. The downside to canister filters is the cost. Canister filters usually run 3 to 10 times the cost of most other types of filters. The canister filter is very basic; a freestanding unit on your floor plugged into the wall. Two tubes, one for intake the other for return, flow between the tank and the filter. A simple electric motor keeps the whole thing going. Additional costs include filter packs (medium) tubing and the occasional impeller. This is an ideal filter system for most tanks over 40 gallons in size.

Lastly I want to go over the last two basic types of filters, Trickle and Fluidized Bed Filters. These two filters are best left to the experienced hobbyist, not the first timer. If this is your first experience with filters I strongly urge you to stick with one of the types already covered. Since the following two types of filters are more for the experienced hobbyist, I have to get a bit more technical here.

FLUIDIZED BED FILTER:

You can NOT take this filter home, set it up by itself, and expect to add fish for up to 2 months, depending on how you initialize the filter media. Fluidized Bed Filters are an extremely efficient high capacity biological filter. Aquatic organisms excrete toxic ammonia as a metabolic waste product, with additional ammonia produced as food and other organic matter breaks down and decomposes. This toxic ammonia (NH3) is converted to another toxic compound called nitrite (NO2) by the Nitrosomonas species of bacteria. The nitrite is then converted to a relatively nontoxic compound called nitrate (NO3) by the Nitrobacteria species of bacteria. This process is known as nitrification . A biological filter is a vessel where nitrification occurs and soluble waste is removed. Beneficial bacteria attach to the media within the Filter, creating a thin film around the sand grains. Water is pumped up through the unit, lifting the sand into a Fluidized bed (hence the name). The beneficial bacteria attached to the media (sand), utilize dissolved wastes (ammonia and nitrite), oxygen supplied by the customary water fall device and other required nutrients from the passing water converting them to relatively harmless nitrate. The sand grains are in continual free fall through the water resulting in an excellent transfer capability between the water and the bacterial film on the media. The enormously high surface area combined with this excellent transfer capability creates the perfect habitat for bacterial growth. In addition, the sand grains bump into each other frequently knocking off excess debris and providing a self cleaning function which allows new areas for bacterial growth. The Fluidized Bed Filter has been tested and proven to supply a high level of effluent water quality and will respond quickly and efficiently to severe changes in ammonia levels caused by over feeding or the addition of too many fish at one time. But it can only do so once the filter has been established, please do not over load or over feed for the first 40-60 days, this is most important.

MATURATION:

The Fluidized Bed Filter can be installed in a short period of time (usually under 1/2 hour), however, the biological maturation takes considerably longer. In most cases, the maturation period should take no longer than 40-60 days. During this period the nitrifying bacteria will attach themselves to the media within the filter. The maturation period can be greatly reduced by introducing live nitrifying bacteria into your filter, inoculating your filter with a small amount of detritus from a mature aquarium, or by adding specific chemicals.

TRICKLE FILTERS:

Trickle filters (also known as wet/dry filters) work on the same principle as under gravel filters, but implement the concept differently. The trickle filter's biological bed is outside of the tank rather than inside the tank as with UGF'S. Aquarium water enters at the top of the filter column and trickles downward through the medium (e.g., stone, specially designed plastic media, fiber materials, etc.), which is not submerged. The nitrifying bacteria inhabit the surface of the medium and process the water as it trickles by. The water then collects at the bottom of the filter column and is then pumped back up into the tank. This design provides for efficient nitrification, as well as good aeration of the water. Some of the better commercial trickle filter designs incorporate drawers for mechanical filtering media, so that the entire filtration system is built into one unit and can be easily maintained.

Trickle filters are particularly well suited for marine aquariums and ponds, where dissolved oxygen levels are low, and freshwater aquariums that use a soil substrate for plantings, making under gravel filtration impossible. Trickle filters do not possess inherently higher nitrifying capacities than under gravel filters. When the most relevant variables are matched, trickle filters and under gravel filters are equally effective. For best operation, the volume of the trickle column should equal about 8 to 10 percent of the tank volume. The water flow rate should be several tank volumes per hour. For the most efficient nitrification, the filter surface area should be designed to yield 0.5 to 1.5 gallons per minute per square foot.

The drawbacks of biological filtration are mostly associated with startup. What is popularly known as new tank syndrome or The Cycle , there is a lag between the time the fish are placed in the tank and the time the populations of bacteria are large enough to process the ammonia and nitrite. But more about The Cycle next month. You can avoid this problem by using doses of ammonium chloride to initiate nitrifying activity in the aquarium and not putting any fish in the tank until the bacteria are established. Use your test kits to monitor this process. Fish are not needed because the bacteria exist everywhere and will become established in the aquarium on their own. Clogging is not a problem with trickle filters.