How To Choose The Best Filter To Keep Your Aquarium Clean

With a particularly magical effect, aquariums and people are fascinated and let us create an underwater world that invites you to dream. However, due to the metabolism of the fish and plants as well as the waste from food, etc., a lot of dirt quickly accumulates in an aquarium.

This dirt not only clouds the view and destroys the optics, but also has a negative effect on the water values so that in the worst case toxins can form. Sooner or later, these toxins will kill all aquarium inhabitants. For this reason, it is important that the water is not only changed at regular intervals but is also continuously filtered. In this article, we will introduce you to different types of filters and how this important aquarium technology works.

The task of an aquarium filter

As the name suggests, the main task of an aquarium filter is to filter and clean the water. In this way, all impurities are filtered out. It doesn’t matter whether it’s plant remains or fish excrement, an aquarium filter, provided it has been selected to match the aquarium, keeps the water clean and ensures good and stable water values. However, there are many different types of filters, which also filter the water in different ways.

In addition to the filter function, most aquarium filters also bring movement into the water, which is caused by the water being sucked in and the filtered aquarium water being expelled. This is also important because many fish and plants need natural water movement. Some filters even offer the option of adjusting the flow rate so that it can be adapted to the needs of the animals living in the aquarium.

In addition to the filter, the plants are also responsible for neutralizing the toxins from the water, so there should always be enough plants in the aquarium, as this is the only way to find the biological balance.

Which filter fits in which aquarium?

Since there are a variety of different filter options, it is not easy to decide on a method. Because of this, you should know each method.

When choosing the new aquarium filter, you should pay attention to different criteria. On the one hand, the filter material plays an important role and must be adapted to the needs of the animals living in the aquarium. And on the other hand, the different filter systems are only suitable for certain sizes or types of aquariums. Furthermore, no small filter, which should be used for a maximum of 100 liters, may end up in a pool with a water volume of 800 liters. The aquarium volume must therefore always match the filter volume of the filter.

What types of filters are there?

There are many different types of filters, all of which have the same task of reliably filtering the water in the aquarium.

The mechanical filter

A mechanical filter filters coarse and fine dirt from the aquarium water. It is suitable both as a pre-filter and as an independent filter system. The individual models convince with a simple change of the filter material and are easy to attach and remove again if necessary. While this filter should have a minimum flow rate of two to four times the water volume for freshwater tanks, it must be at least 10 times the volume for seawater tanks. For this reason, many aquarists change the filter substrate every week, but this means that the mechanical filter can never function as a biological filter with many important bacteria because these are destroyed during cleaning. The internal motor filters, for example, which are available in numerous designs, are particularly suitable as mechanical filters.

Trickle filter

Trickle filters are rarely used. These work as so-called “super aerobes”. The water is applied to the filter material, which means that it naturally has contact with air and is then fed into a separate basin. The water is now pumped back from this basin. However, trickle filters only work effectively if at least 4,000 liters of water per hour run over the filter material, which is rarely the case.

Anaerobic filters

An anaerobic filter is a good method of biological filtration. This filter works without oxygen. With such a model, the filter material must be flushed with low-oxygen water, which is only possible if the water flows slowly. If the water flows through very slowly, the oxygen will have completely disappeared after just a few centimeters in the filter bed. In contrast to other filter options, however, only nitrate is broken down, so that you cannot convert proteins and the like into nitrate and then break them down. For this reason, these filters can only be used additionally and are unsuitable as stand-alone filters.

Biological filter

With these special filters, the bacteria in the filter clean the water. Millions of small creatures, including bacteria, amoebas, ciliates, and other animals, live in these filters and feed on the organic matter in the water. The organic matter is removed or modified so that it can be added back to the water. These bacteria and other small creatures can be recognized as brown sludge on the filter materials. So it’s important not to wash them off over and over again, they’re good for the aquarium, and as long as enough water flows through the filter and it doesn’t get clogged, everything’s fine. Proteins, fats, and carbohydrates, which can all be found in aquarium water, are the main food for microorganisms. These are converted into nitrate and carbon dioxide. The biological filter is also suitable for all aquariums.

External filter

This filter is located outside of the aquarium and therefore does not disturb the optics. The water is transported through hoses, which are available with different diameters, to the filter, which is usually located in the bottom cabinet of the aquarium. The water now runs through the filter, which can be filled with different filter materials and is filtered there. The filter material should also be selected individually according to the stocking. After cleaning, the water is pumped back into the aquarium, which naturally brings movement back into the tank. the external filters are of course advantageous because they do not take up any space in the aquarium and do not impair the visual image.

Internal filter

In addition to the external filters, there are of course also internal filters. These suck in the water, clean it inside with individually selected filter material and then return the cleaned water. The internal filters naturally have the advantage that no hoses are required. They are ideal for use as flow generators and are available in numerous sizes. While some models can be used as pure aerobic filters, there are also models that filter part of the water anaerobically and the other half aerobically. The disadvantage, of course, is that these filters take up space and have to be completely removed from the tank each time they are cleaned.


Whichever aquarium filter you choose, it is important that you make sure that you buy it in a sufficient size. It is therefore better to opt for a larger model, which may purify more water, than for a filter that is too small and cannot handle the amount of water in your aquarium. It is also important that you always respond to the individual properties and needs of the filters so that they have a long service life and always reliably keep your aquarium water clean.

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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