Why do you need a Filter?

It is possible to maintain an aquarium without any filtration at all (natural bio-system) by having few fish in a relatively large quantity of water, and lots of plants. However, most of us would not be content with just a few fish in a large tank, and having lots of plants may not be possible with certain species of fish. Therefore, some method of filtration is necessary to maintain the water quality. We will now go on to discuss the various types of filtration available to the hobbyist.

Air-Driven Sponge Filters

A very basic, cheap, but very effective filter, consisting of an uplift tube with one or more sponges attached at the bottom. Requires an air supply (aquarium air pump) to operate it. Only really suitable for small tanks up to 61cms (24 ins). The sponges should only be cleaned out gently in old aquarium water during water changes, as beneficial bacteria living in the sponge material would be destroyed in chlorinated cold tap water. A very useful filter for breeding tanks as the fry will not be sucked into the filter.

Air-Driven Internal Box Filters

Usually square, clear plastic containers which sit on the floor of the aquarium, which require an air supply (aquarium air pump) to operate them. The container is usually packed with filter wool, but other filter mediums such as carbon can be used. Cheap but effective, if perhaps a little unsightly within the aquarium. Single units only suitable for tanks up to 71 cms (30 ins), but more units could be used for larger tanks.

Undergravel Filters

This consists of a plastic plate (or more than one inter-locking plates) which is positioned inside the aquarium on the glass base, and covered with about 2 ins of gravel. One or more uplift tubes (depending on the tank size) are connected to the plate generally in the tank corners where they are not so conspicuous. The uplifts are either air operated or fitted with powerheads, which draw the tank water down through the gravel, along under the plate, and up the uplift tubes and return it to the aquarium. The gravel bed, being fed with oxygenated water containing nitrites (produced by food and fish waste) becomes colonized with a vast number of beneficial bacteria, which break down the nitrites into much less harmful nitrates. Undergravel filters are very efficient biologically, but the solid waste which collects within the gravel should be removed occasionally using a gravel cleaner when carrying out a partial water change. A very popular method of aquarium filtration.

Electric Internal Power Filters

Produced by a wide variety of manufacturers, electric internal filters are very easy to use - place it in the tank, plug in and switch on. There are sizes to suit all aquariums up to 120 cms (48 ins), beyond that, more than one unit would be required. A big advantage is the lack of noise produced when running. All electric internal filters use a sponge as the main filter medium, which should be cleaned out occasionally in old tank water whilst doing a partial water change. In addition to the sponge, some makes of filters have facilities for adding carbon, whilst others can be fitted with a carbon sleeve instead of the sponge. Another facility available on most internal filters is the ability to suck air from above the water, and vent it with the filter output water, thus producing extra aeration.

Electric External Power Filters

These are canister type filters which would be positioned outside of the aquarium below the tank water level, as a syphon effect is required for the water to be fed to the filter. The filter is connected to the aquarium by two flexible plastic tubes, one supplying tank water to the filter, the other returning the filtered water back to the tank through either a jet pipe or spray bar. These are the most expensive types of filter, and are generally used for larger tanks. The great advantages are the increased flow rates, and the fact that different filter mediums (including sponge, ceramic tubes, carbon, ammonia removers, filter wool, peat etc) can be used in the containers which are fitted in the canister.

Fluid Filters

A relatively new idea for biological filtration. A canister filled with aquarium water is position on the outside of the tank, and contains a quantity of special sand. A pump or powerhead is required to pump the aquarium water in at the bottom of the canister, and out and back to the aquarium from the top. This causes the sand within the canister to be constantly in suspension, thereby allowing a far greater build up of beneficial bacteria on and in the sand particles than could ever be achieved with a normal undergravel filter bed. The flow rate of the water through the canister is critical and has to be adjusted to ensure the sand stays in suspension, but does not reach the top and end up being deposited back into the aquarium. The fluid canister filters are expensive, and added to that is the cost of the pump or powerhead. These filters are generally used by hobbyists keeping tropical marine tanks.