As a newcomer to the aquarium hobby, you may not be aware that as well as making your aquarium water clear, so that you can see your beautiful fishes, the main task of a filter is to break down the waste that fishes produce. It is the friendly bacteria that live in your filter media, known as nitrifying bacteria that do this amazing job. They colonize the media in your filter, and their success is completely reliant upon it. The higher the surface area of your media, the greater the efficiency of the filter, and provided they have a plentiful supply of oxygen and nutrients, and kept free of debris, they will thrive.



There are many types of aquarium filter available, although you only need to consider the three main types for your basic set up.

Undergravel:

The undergravel system consists of undergravel plates that cover the whole of the bottom of the aquarium; these plates are full of small slits that allow water through them. Uplift tubes are inserted into the plates vertically at each end of the aquarium. The plates are then covered with about 2-3ins (5-8cm) of gravel, the gravel works as the medium.

The system can either be air operated, in which case, an electrically operated air pump delivers air through a small tube, which is placed down the uplift tube, as the air exits the small tube at the bottom of the uplift, it rises in bubbles at the same time drawing water with it from beneath the undergravel plates, therefore the water is filtered as it passes through the gravel and beneath the plates and then up the tube to be circulated again.

The alternative to air operated, and much preferred, are powerheads. These are small electric water pumps that sit on top of the uplift tubes. The way that the water is filtered is the same as the air operated system, however, the powerheads can circulate a much greater volume of water, and it is this extra power that is necessary for an undergravel system to work well. They are also much quieter, and they vary in size depending on the amount of water they are required to circulate. For a basic community aquarium this should be at least 3 times per hour.

Internal filter:

These are normally smaller than their external counterpart, and generally contain only one filter medium, usually a foam structure. They are powered by pumps similar in design to the previously mentioned powerheads but usually an integral part of the filter. As their name implies they operate from within the aquarium, water is drawn into the filter compartment by the pump where it passes through the foam, (this is where the nitrifying bacteria get to work), the water then returns to the aquarium from the pump outlet to be recycled again.

This type of filter is the easiest of all to install and maintain. Before choosing an internal filter as the ONLY means of filtration, think carefully about the size of your set up; remember water quality relies heavily on filtration.

External filter:

These are generally larger than internals and contain at least two mediums, therefore biological capacity is increased, and it is possible to add different mediums to carry out different tasks, thereby being more adaptable to individual needs.

Although based on the same principle as the internal filter, these pressurized systems require plumbing-in and are normally situated remote from the aquarium, such as the cupboard of a purpose built aquarium cabinet. External filters are also available in various sizes, and are relatively easy to maintain, although you should always keep the pipe connections maintained for obvious reasons.

Air Pumps:

As previously mentioned air pumps can be used in a limited capacity to power an undergravel filtration system, but by enlarge they have been superseded by powerheads. Air pumps vary in size and your choice would be dependent on the number of features you wanted run, and although a cascade of bubbles rising to the surface may have a pleasing effect on the eye, the main reasons for aeration are rather more practical.

An air pumps primary function is to inject air bubbles into the aquarium; what you are aiming for is to use a diffuser that produces extremely tiny bubbles. If you have ever noticed bubbles rising in water you will have realized that the larger the bubble, the faster it rises to the surface.

The idea is to have the bubbles rise to the surface as slowly as possible; this then gives the natural process of absorption the best opportunity to work. The longer the bubbles take to rise to the surface the better the chance is of oxygen being absorbed from them. However, that is only part of the process; the slowly rising bubbles are also able to carry waste gases, such as carbon dioxide expelled from your fishes, to the surface and into the atmosphere, which in turn reduces its effect on pH.

It is important to note that the oxygen absorbed in this way is only a tiny proportion of the requirement needed for your living aquarium. It is from the surface area of your aquarium water that the most oxygen is absorbed, this is the very reason for having an aquarium with as large a surface area as possible; this gives a greater surface area for any given volume of water, which aids the absorption of oxygen and the "gassing off" effect of the carbon dioxide.