Internal and External Filters in the Aquarium

Every aquarium represents a highly sensitive ecosystem. An aquarium filter is required so that life in your underwater world is possible. This takes on the vital task of keeping the water clean for the inhabitants of the pool. Find out important information about internal and external filters here.

The function of the filter

The function of the aquarium filters is always the same: on the filter substrate of the aquarium filter – just like in the substrate – there are microorganisms and bacteria that feed on harmful substances dissolved in the aquarium water. In addition, the filter sorts out suspended matter such as food or plant residues, thereby keeping the water clear. In short: the filter sucks in the aquarium water, cleans it, and then releases it again in a cleaned state.

A good filter thus ensures mechanical, biological, and chemical filtering in equal measure: the mechanical filtering removes the suspended matter, while the necessary bacterial population can develop on the biological filter. Additional chemical filtering using special filter media can prevent water discoloration and unpleasant smells or adjust your water values ​​to the needs of the aquarium inhabitants.

In order to “metabolize” as many harmful substances as possible, a large filter surface is advisable so that a large bacterial lawn can form on the filter substrate. Because of the larger the filter volume, the more filter bacteria and the better the degradation of pollutants. The flow rate – i.e. how much water flows through the filter per minute – is less important. Here it is sufficient to observe the rule that the water content of the aquarium should be circulated about twice an hour. Through this water circulation, the temperature in the aquarium is evenly distributed, the aquarium plants receive the necessary nutrients, the aquarium is supplied with sufficient oxygen and the pH value is maintained or increased. In addition, the water circulation creates a current that offers the fish almost natural water conditions.

Internal or external filter?

When setting up your aquarium, the first question you are faced with is: internal or external filter? When choosing, the most important thing is the aquarium. The internal filter is suitable for small aquariums with few fish and is characterized by its easy handling. It is effortlessly hung up in the aquarium with suction cups or is hidden in the bottom of the aquarium. The water is sucked up close to the ground and given off in a cleaned state just below the surface of the water.

For large to very large aquariums (from 100 liters), however, an external filter is useful, as this also has a higher cleaning performance with its larger filter volume. It is usually located in the aquarium base cabinet and is connected to the water from the outside by hoses, which makes maintenance and cleaning a little more labor-intensive. Even if the installation seems difficult at first, the external filter has the advantage in the long run that additional technology such as UV sterilizers or slow filters can be conveniently installed between the hose lines. In addition, it does not take up any space in the aquarium itself, which means that the inhabitants of the tank are given more living space.

More unusual, but also available in pet shops, are more special variants such as the backpack filter or filter devices that are housed in the cover above the aquarium.

Cleaning the filter

“Cleanliness is definitely good if you overdo it, harm yourself” is a well-known saying that can be applied to filter cleaning. If the filter is cleaned weekly or even more often, the necessary bacteria that are responsible for destroying the harmful substances cannot settle. Filter cleaning is only necessary if the flow of water is no longer guaranteed. The substrate should be briefly rinsed with tempered aquarium water or lukewarm tap water (under no circumstances use hot or cold tap water) so as not to remove the entire bacterial population. Cleaning agents should definitely be avoided – even when cleaning the plastic parts. In order to preserve the bacteria, it is also advisable to carry out the partial water change and the filter cleaning at different times when cleaning the aquarium.

The technology has to “live”

With a new filter, there are of course no bacteria on the filter substrate. In order for the bacterial population to settle and the ecosystem in the aquarium to change, it should first be operated without fish for a while. Only when the ideal living conditions have been created in this way, nothing stands in the way of the aquarium inhabitants moving in. If the underwater world is to be relocated to a new aquarium, the old filter should not simply be disposed of and replaced with a new filter, but should rather be used due to the existing bacterial population. If a new filter is still required, it makes sense to simply let it “run” on the old aquarium before moving, so that bacteria can also settle on the new filter substrate. It is also possible to use the old filter material in the new filter after moving: Here, however, the filter capacity may initially be reduced, as the bacteria still have to get used to it.

Mary Allen

Written by Mary Allen

Hello, I'm Mary! I've cared for many pet species including dogs, cats, guinea pigs, fish, and bearded dragons. I also have ten pets of my own currently. I've written many topics in this space including how-tos, informational articles, care guides, breed guides, and more.

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