What Does An Aquarium Filter Do?

Understanding filters and how they assist the effective functioning of your fish tank is vital as a fish keeper. We have put together a simple guide on filters and how they work!

What are Fish Tank Filters For?

There are three different things that an aquarium filter can do: biological filtration, mechanical filtration and chemical filtration.

Biological Filtration biological filtration is the process of converting the ammonia produced by fish into a harmless nitrate. This is the most important function of a filter and the reason why you must have a filter in your fish tank.

Mechanical Filtration – mechanical filtration will remove physical debris such as fish waste and leftover fish food.

Chemical Filtration – this will remove certain chemicals from the water, but you will have to check that you have this type of filtration, as it depends on what filter media you have.

However, the main purpose of the filter is filtration in the biological sense, as neither mechanical nor chemical clean the tank in the true sense of the word.

There are many different types of aquarium filters available, so it can be difficult to know which one is the right one for you. We stock four different types of filter:

Hang On Filters

Ideal for small to medium tanks, hang on filters hang on the back of the tank and create a waterfall as the water is thrown back in the tank. They are inexpensive and therefore commonly used. However, they can be noisy, and because the intake and outflow are close to each other, it ends up taking in water it has already filtered. Because of this, it is recommended that you look carefully at the size of the tank that the filter is rated for, and make sure that you don’t exceed it.


Hang On Filter

External Aquarium Filter

External filters are at the high end of filtration – they draw the water out of the aquarium into an external box or canister, where the water is pushed (by a water pump) through a series of different filters, and then back into the tank. These types of filters usually provide you with all three types of filtration: chemical, biological and mechanical, depending on what kind of media you’re using. External filters are good for medium to large tanks as they are a very efficient method of filtering your tank water if maintained correctly.

Take a look at our external aquarium filters.

EF 1400 External Filter

Internal Fish Tank Filter

As the name suggests, these filters go inside the tank rather than outside of it. They are usually quieter than external filters; particularly hang on filters – as they don’t have the waterfall effect. Internal filters usually sit in the corner of the tank, just below the water’s surface. they usually use sponges to filter debris, and to cultivate bacteria for biological filtration. Water is drawn up through the bottom of the filter and through the sponge. They can be used in small to medium tanks, though be sure to check the filter’s recommendations.

Browse our internal filters here.

Internal Filter

Undergravel Filters

Undergravel filters use the gravel as a filter. They usually come in the form of a plastic slatted tray that keeps the gravel off the bottom of the tank, lift tubes to deliver water and an air pump to move the water. The gravel acts as a mechanical and biological filter. They are ideal for beginners, or those with very small or awkwardly shaped tanks.

Find our undergravel filter product page here.

Boyu Under Gravel Filter