Freshwater Aquarium Filter Systems Explained

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     Of all of the equipment used in an aquarium, none is of more importance than the filter. Although even the most novice of aquarium enthusiasts may be aware of this fact, the wide variety of aquarium filter systems that are available on the market can cause some confusion.

In order to avoid such unnecessary confusion, it is best to first analyze the three primary roles of aquarium filter systems. These are: Mechanical, chemical and biological filtration.

Mechanical Filtration

This type of filtration system is the most basic and easiest to understand. Mechanical filtration simply removes visible particles that are present in the water.

Chemical Filtration

In order to properly understand chemical filtration, it is easiest to view it as the logical extension of mechanical filtration. Whereas, mechanical systems remove the waste that is visible, chemical systems remove the waste that has dissolved into the water and therefore invisible. Chemical filtration normally relies on activated carbon or zeolite to remove the waste.

Biological Filtration

This method of aquarium filtration harnesses the power of beneficial bacteria to propagate the nitrogen cycle in your aquarium in a fashion similar to that found in natural maritime ecosystems. As clarity is essential to understand the fundamentals of this biological filtration, it is important to focus on its basic functionality and not to get lost in overly academic explanations of its performance.

Quite simply, biological filtration systems allow for different types of beneficial bacteria to be present within the aquarium. In turn, some these microorganisms convert the ammonia that comes from the fish waste into nitrites, which in turn are converted by other bacteria into nitrates.

Although nitrates are still harmful to fish in large concentrations, it is easier to monitor and to remove through the simple act of regularly scheduled partial water changes.

Filter Types

Now that one has a general understanding of the different filtration roles performed by aquarium filter systems, it is time to look at specific types of filter units.

Airlift filters are quite common and incorporate mechanical, chemical and biological elements in their functionality. All airlift filters function submerged in the aquarium and rely on airlift, which creates a flow of water through the filtration media. This airlift is commonly achieved with air pumps or in some instances air stones.

Of these airlift filters, corner filters are among the least expensive. They use a layer of activated carbon and filter wool to perform the mechanical, chemical and biological filtration of the water that passes through it. They do, however, pose the need for frequent cleaning of the filtration media and can actually release dangerous contaminants back into the water if neglected for too long.

Another inexpensive variation of the airlift filter is the sponge filter. These filters are similar to corner filters except that they use a sponge based material as opposed to filtration wool and have no active component to generate chemical filtration, such as activated carbon or zeolite. Sponge filters can be effective with aquariums housing a small fish population or in breeder tanks, as the use of a sponge as a filtration medium prevents fish fry from getting needlessly trapped in the filter. Although sponge filters are quite effective with biological filtration, their lack of chemical filtration and less than stellar mechanical filtration make them more suited for aquariums with smaller fish populations and are not ideal candidates for larger fish populations.

Apart from airlift filters, there are also undergravel filters. These aquarium filter systems force water in a downward motion through the aquarium gravel itself to achieve its mechanical filtration. This same action allows for beneficial bacteria to populate the gravel substrate, thus achieving biological filtration. The water that has been passed downward through the gravel is then returned to the tank via uplift tubes, which in turn pass the water through activated carbon for a chemical filtration effect.

Undergravel filters can be quite effective, but do require a strong focus to be placed on the vacuuming of the gravel substrate. Failure to do so not only compromises the mechanical filtration role of the undergravel filter, but also places in danger the beneficial bacteria and their subsequent biological filtration role.

In the end, you should select the best aquarium filter that you can afford. Do not opt for the least expensive, but keep it within your budget. Keep in mind the maintenance required by the filtration system that you select; and make certain that you can adhere to it. Even the best filters will fail if you do not perform the expected maintenance. Remember, as long as you understand the mechanical, chemical and biological roles involved in aquarium filter systems, it will be easier to select a filter for your aquarium and to ask the right questions when buying it.