Aquarium is a vivarium which has at least one transparent side and is
used to keep aquatic animals, invertebrates and amphibians. Generally,
aquariums are used to keep fish. People are of the opinion that
maintaining an aquarium is a tedious job but if done with care it is not
so difficult to maintain. Nowadays aquarium filters, are the latest type
of aquariums which come with filter facility making it easier to clean
the aquarium. Following are some of the important features and functions
of aquarium filters:

* They serve as critical components of marine aquarium and freshwater
* They help to remove chemical and physical waste products and help to
maintain the cleanliness of the tank
* They help to support life in aquariums by maintaining good hygiene in
the tank.
* Nitrogenous wastes are also cleaned by the filter and thus it helps to
maintain a balance of nitrogen in the aquarium.
* With help of mechanical filtration, various harmful particles can be
removed from the water column. These particles may contain uneaten food
materials, algal debris, faeces, dead plants etc.

Aquarium filters come in a variety of types which will suit all your
requirements. External and internal filters are the two major types.

An external filter is a commercial type of filter which removes all the
water from the aquarium. Once the water is removed, it goes through
various levels which filters the water and the filtered water is filled
back in the aquarium. The external filters are handy and require less
maintenance. Following are some of the commonly used external aquarium
filters:

* Canister filters are used to filter greater quantity of waste
materials. This filter offers much better flexibility than the other
filters. There is a pipe found in the bottom of the filter which allows
the entry of the water. The water is filtered as it passes through some
filter material and is pumped back in the aquarium with the help of tan
electric pump which is fitted on the top of the canister. The only
drawback of the canister filters is that they are more expensive in
comparison to the other filters and the tubes of these filter are long in
size so they are difficult to clean.
* Diatom filters have some limitations that they can be used only for
sporadic cleaning of tanks and cannot be operated continuously on
aquariums. However, this filter is used for removing extremely fine
particles and it can easily remove the ultra fine particles from the
water column.

Internal filters are filters which are fitted in the aquarium itself
which may make use of the electric pump or the internal power lifter. For
cleaning they make the use of the sponge filter, foam cartridge filter
etc. Following are some of the commonly used internal filters:

* Airlift filters, they make the use of sponge filters and corner
filters. Both these filters used have the same mechanism. The filters are
generally placed at the corners of the tank. They are suitable for
cleaning the aquariums of smaller sizes.
* Under gravel filters comprise of one or more number of tubes. The
under gravel filters consist of a porous plate which is fitted at the
base of the aquarium. These filters are driven by means of air
displacement. Water is forced out of the uplift tube due to the air
stones present at the base. This creates negative pressure on the uplift
tube. Once the pressure is built the percolation of water takes place
from the gravel which then acts as a filtering material. The greater the
flow of water, the greater is the amount of filtration.