Do I need an aquarium filter?

It is the role of the aquarium filter to maintain a stable and safe water quality within an aquarium.
If the water quality is ideal then the fish will thrive and be less likely to develop health problems.
An aquarium filter is effective removing solids and breaking down soluble waste produced by the fish.
Once installed, a filter immediately acts mechanically, removing solid suspended waste from the water,
eventually maturing into a ‘living system’ holding beneficial bacteria which break toxic waste products
(ammonia) excreted by fish into less toxic nitrites. Additional bacteria breakdown the still potentially
lethal nitrites into nitrates.

If the filter is too small for the aquarium or is not cleaned regularly then the bacteria will be unable
to breakdown the toxic wastes leading to a positive ammonia and/or nitrite reading, stressing the fish
leading to health and disease problems. Similar problems will arise if too many fish or too much food
is added to an aquarium.

What types of filter are there?
There are many different makes and models of aquarium filter available, but most of them can be placed into 1 of 3 types:

  1. Under Gravel Filters
  2. Internal Power Filters
  3. External Power Filters

A very economical and reliable filter, which is ideal for the beginner as it requires little
maintenance and is easy to install. A special undergravel filtration plate is placed on the bottom of the
tank under a 2-3″ layer of gravel. An uplift pipe is fixed to one corner and water is drawn up the pipe by
an airstone placed at the base of the uplift or by a powerhead (a small submersible electric pump) which is
fixed to the top of the air-lift. In this way, dirty water is pulled down through the gravel and returned
clean through the uplift.

Undergravel filters are easily cleaned using a siphon tube fitted with a gravel cleaner which removes
solid debris collected in the gravel, leaving the gravel behind.

Although they are quick and easy to install, undergravel filters do make growing plants quite difficult.

Internal power filters are ideal for all sizes of tanks. They sit in the corner
of the tank and consist of a powerhead attached to a container of filter media, usually foam. Water is
drawn through the bottom of the filter by the powerhead and pumped back into the water via the outlet.

Maintenance involves cleaning the foam every 1-2 weeks, rinsing it in a bucket of aquarium water rather than
raw tapwater so as not to harm the beneficial bacteria in the foam.

Some internal filters now also incorporate a heater, which tidies up the appearance of the tank and distributes
the heat effectively through the aquarium.

Although maintenance of an internal power filter is carried out more frequently than an undergravel filter,
it can be cleaned very easily without too much disruption to the aquarium.

External Power Filter
Unlike the previous 2 methods of filtration, external power filters sit outside the tank, holding filter
media within a canister. The water is drawn from the aquarium through a siphon tube and passed through one
or more different types of filtration media before being pumped back into the aquarium. Water can be returned
via a spraybar to aerate the water.

This is usually the most expensive of the 3 types of filter but it allows a wide range of different media to
be used, without taking up valuable aquarium space or looking unsightly, some are even supplied with an
integral heater. External power filters will only usually require cleaning every 2-3 months and can be
carried out without disturbing the fish or plants.

Is an air pump required?
In most aquaria, an air pump is optional unless it is used to drive an undergravel filter. If an aquarium
is stocked and filtered correctly then an air pump should not be required, however, it is a useful addition
for a new fishkeeper as it adds an extra level of safety should fish be overfed or overstocked.

Air pumps can be fitted with an airstone to diffuse air into the water. Some people like this visual effect
while others prefer their aquaria to look more natural without a stream of rising air bubbles. Air pumps can
also be used to drive ornaments such as divers and treasure chests, appealing to the younger aquarists.

Undergravel Filter


  • Cheap
  • Straightforward installation
  • Effective


  • Must be installed when aquarium is first set up
  • Cleaning can cause fish an inconvenience
  • Requires an air pump or powerhead to run it

Internal Power Filter


  • Provide a rapid turnover of water
  • Able to remove fine particles


  • More expensive than UGF
  • Difficult to hide in an aquarium

External Power Filter


  • Very versatile with many media options
  • Once set up, they are reliable and efficient
  • Can be cleaned out without disturbing fish and plants
  • Do not take up in-tank space
  • Require cleaning every 2-3 months


  • Relatively expensive
  • Can be tricky to install
  • Space for filter outside tank is required

Kill blanketweed and string algae.