Choosing the filter.

A selection of internal filters available from Aquatic FanaticWhen it comes to filtration there are a number of choices, which the beginner can find confusing. The filter is perhaps the most important piece of equipment for your aquarium and is essential for keeping the fish healthy and the aquarium clean. The filter keeps the aquarium clean by removing waste products from the water like uneaten food, decaying plant matter and biological waste produced by the fish. The following table attempts to explain the differences in filtration types.


Filter Type Description Pros Cons Mechanical* Biological* Chemical* Typical Use
Under gravel (operated by an air pump). The filter fits in the bottom of the tank under the gravel. An air pump powered uplift circulates the water through the gravel trapping particles and clearing the water. The gravel becomes the home for bacteria which consume fish waste. Discreet.



Can use carbon insert for chemical filtration.

Excellent biological filtration.


Difficult to clean.

Not very good for growing plants.

Not ideal for digging fish.

Noise from air bubbles.

Very good.



Very good. Very good but can only be used with an air pump. Popular, traditional filter. Should only ever be cleaned with a gravel cleaner.

Under gravel filters come in all sizes to fit any tank.

Under gravel (operated by power head electric pump). As above, except a power head circulates the water through the Under gravel. As above except almost silent running.

High turnover of water and increased water circulation.

Same weaknesses as above except carbon cartridges cannot be used. Very good. Very good. Not available. Seen by many as an improvement over air operated under gravels, especially if noise is an issue.
Internal Power Filter. A water pump circulates water through a foam media which traps particles and becomes biologically active to treat fish waste. There is also an option to pass the water through a chamber full of carbon to remove other toxins. Very easy to look after and to clean.

Quiet running.

Excellent mechanical filtration.

Care must be taken not to over clean, should only be washed in mature aquarium water.

Takes up aquarium space therefore more obtrusive.

Very good. Very good. Very good. Now the most popular type of first filter.

Available in sizes to suit aquariums up to 4ft.

Thermo-filter As above but the filter also houses a heater which brings the water up to the correct temperature As above.

Only needs one plug instead of two!

As above. Very good. Very good. Very good. Popular for smaller aquariums.


External Power Filter (Canister). Water is syphoned out of the aquarium into a canister underneath  the aquarium, full of filter media. It is then pumped back into the aquarium. The most unobtrusive filter.

Very versatile.

Use any combination of filter media.

Infrequent, easy cleaning.

Silent running.

Relatively expensive. Very good. Very good. Very good. Canister design has improved so they are now very user friendly.

Now appeal to beginners, as well as experts.

For all types of aquarium over 2ft.

Sponge Filter (needs air pump). Air powered uplift circulates water through a sponge where it is mechanically and biologically filtered. Relatively cheap.

Excellent for raising fry.

Ideal for smaller sized aquariums.

No chemical filtration.

Care must be taken when cleaning sponge.

More obtrusive.

Very good. Very good. Not available. Only used in aquariums up to 2ft.

Ideal back-up filter for breeding, quarantine or hospital aquarium.

Box Filter (needs air pump). Air powered uplift circulates water through a small box of media of your choice. Relatively cheap.

Good back-up filter for carrying out specific tasks, i.e. carbon filtration.

Limited capacity.


Depends on which media you pack into the box. Depends on which media you pack into the box. Depends on which media you pack into the box. Best used as a supplementary filter. Or for smaller temporary aquariums for breeding etc.

A selection of external canister filters available from Aquatic Fanatic*Mechanical - this is the removal of suspended particles in the water, keeping the water clear and the aquarium clean, so that you can see your fish!

*Biological - essential bacteria colonise on the filter media. These bacteria consume the waste material which fish excrete, so purifying the water.

*Chemical - certain filter media, such as carbon and zeolite directly absorb certain soluble dyes and other toxins from the water.

Back to setting up or on to positioning the aquarium


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