Internal Or External Filter For The Aquarium?

When it comes to aquarium equipment, ten people have at least eleven different preferences. The variety of design options and the increasingly extensive product range of relevant retailers also allows experienced aquarists to keep fish in a multifaceted way. Of course, not only fish end up in the aquarium, shrimp, snails, crabs and pure aquascaping projects are also very popular. For each individual aquarium, it is therefore necessary to weigh up exactly which technology or which accessories are required. The requirements of the underwater inhabitants naturally have higher priority than the personal preferences of the owner, although the latter can provide the finishing touches. For example, there is no question that a filter is necessary. However, whether it is an internal or external filter for the aquarium depends on numerous factors, the personal preferences just mentioned and last but not least on various issues such as the available space and the maximum budget for the purchase. You can find out which type of filter is best suited for which aquarium in this article.

Aquarium filter – immersed in the underwater world of technology

In almost every aquarium there is constant water circulation, modeled on the natural conditions on site, in order to enable the inhabitants of the tank to live as species-appropriately as possible. This results in very different strengths and heights of the currents, bubbles and also particularly still waters. The movement is usually accompanied by filtration at the same time. In other words: the water is sucked in by a pump, filtered and fed back into the circuit. Water movement and cleaning can therefore be optimally combined.

Accordingly, the different aquarium filters pursue different approaches. Some need high performance to move or circulate a three-digit volume of water, while others require less power but more complex filter properties. The demands are therefore quite varied and not always clear at first glance.

The role of the filter in the aquarium

For the aquarium, water filters primarily take over the permanent treatment and cleaning of the water. It is important to filter waste materials, uneaten food and legacies from the fish and not to let them get back into the tank until the filter is cleaned again or the pollutants have been converted. A large number of filter types, especially for aquariums, are therefore based on microorganisms that settle on the filter material and carry out additional conversion processes, for example from nitrogen to oxygen, ammonia to nitrate and the like. At the same time, certain water values ​​can be manipulated via the filter material, for example the pH value.

But the strength with which the water is circulated, the location of the intake and the outlet and other factors also play a major role in choosing the right aquarium filter. Thus, aquarium filters work on different levels and have specific tasks accordingly. This in turn results in different designs and concepts:

  • Internal filters such as the Hamburg mat filter, bottom filter, protein skimmer and foam cartridge filter;
  • External filters such as the sand filter, trickle filter and backpack filter;
  • Additives such as peat, microorganisms, chemical substances and specific filter materials.

Depending on whether an internal or external filter is used, its tasks in the aquarium can be mastered differently. However, the decisive factor is always the volume of the aquarium, how much space is available and which species of fish and other inhabitants should live in it.

Is it also possible without a filter?

If no filter were used to treat the aquarium water, the water quality would all too quickly reach a point where it not only became uncomfortable for the inhabitants (both animals and plants), but also downright dangerous to their health and even life-threatening. Since an aquarium tank is a closed system, no external influences, for example, can collect groundwater, allow rain or bring in microorganisms. In nature, it is precisely these who take care of the filtering: the soil, the plants and the microorganisms.

The soil screens out debris and returns clean groundwater to the hydrological cycle, which returns as fresh rain. Plants and microorganisms convert toxins and waste products so that they no longer have a toxic effect, but even become helpful to the point of being essential for life. The photosynthesis of the underwater plants alone lowers the nitrogen content and supplies the animals with the oxygen they need to breathe.

If there were no filter functions in the aquarium, life in it would soon no longer be possible. Plants and the small amount of sediment alone cannot filter the aquarium sufficiently. Algae would form too quickly, which in turn would attack the panes and the surfaces of the leaves and consequently prevent the light supply to the plants. These would then die and in turn release toxins from putrefaction processes into the water. Parasites would find the best conditions there, but after all nobody wants them in the aquarium. Especially since ornamental fish rarely have enough immunity and defenses to endure such a load permanently without consequences.

Partial water changes can and should be carried out regularly to support the water quality, but these are only partial amounts. Replacing the entire water would have an equally negative impact on the biotope aquarium. The fish are too sensitive, the water parameters too unstable and the quality changes too quickly for permanent filtering to be dispensed with.

Types of filters for aquariums

Each type of filter has its own characteristics. This begins with the construction and the space requirement. Internal filters are logically installed in the aquarium, external filters outside and only the intake pipe and outflow are in the water. So the question arises where the placement makes the most sense. At the same time, the size of the filter and whether it fits the size of the pool or the water volume is decisive, i.e. whether the capacity is sufficient to move the amount of water.

There is no one-size-fits-all solution for all aquariums, and with good reason. Each tank and each species of fish has its own requirements, which must be met to the best of your knowledge and belief so that everyone can enjoy the aquarium – inside and outside.

Internal filter – handy but difficult to reach

Most beginners opt for an internal filter. Why? Because these are easier to handle, they are usually even included in complete sets for aquaristic beginners. With the internal filter, the entire construction is in the water. Except of course the power supply.

A suction opening draws in the water and pumps it through filter materials of different coarseness. This can be, for example, fleece, foam, activated carbon and special filter floss. The variously sized suspended particles and impurities get caught in it and are regularly removed together with the filter material. The cleaned material is then used again and that’s it.

In addition, the microorganisms already mentioned colonize the filter material. They also accumulate on the surfaces and feed on leftover food and excretions. Through this process, toxins and pollutants are converted and flow back into the water as healthy nutrients with the current through the diffuser.

The advantages of internal filters:

  • They don’t take up any space outside the aquarium
  • They are usually cheaper to buy
  • Various filter materials can be used as required
  • Internal filters are very quiet / low-noise
  • They are also often more energy-efficient because they have low power consumption

The disadvantages of internal filters:

  • Internal filters are more difficult to reach for replacing the filter parts, for maintenance and
  • cleaning, and may even have to be lifted completely out of the water
  • The performance is often limited because the filters are quite small
  • Internal filters sometimes impair the optics in the aquarium and are sometimes perceived as
  • Annoying for viewers
  • And of course, they take up space in the aquarium, which the fish in turn lack if they are not used as a design element at the same time

For which aquariums internal filters are suitable:

  • Due to their performance deficits, internal filters are mainly used in small to medium-sized pools;
  • They are mainly suitable for nano tanks in the form of bottom filters so that they do not fill the already small space in the tank too much;
  • In combination, internal filters are also an excellent addition to filtration in larger tanks as a secondary solution;
  • In rearing tanks, internal filters are usually the gentler solution without the risk of the young fish getting caught in a suction device.

External filter – powerful but noisy

As the name suggests, external filters are placed outside the tank and, with a little skill, can even disappear without a trace in the base cabinet or in a niche next to the aquarium so as not to disturb the field of vision.

The filter is connected to the aquarium via an intake pipe and an outflow. The suction device is usually protected with a basket or something similar so that no fish or larger plant parts are sucked in. The outflow, in turn, can be installed flexibly and independently of the suction device and can thus either provide an overflow or generate it in the lower part of the pool.

Just like with the internal filter, different filter materials can be used, which are also populated with microorganisms due to the permanent water flow. The only drawback: If the aspirator is installed directly on the water surface and this falls off, for example due to excessive evaporation, the pump draws air. This can not only damage the technology as such, the water quality also suffers promptly from the lack of flow and filtering.

The advantages of external filters:

  • They hardly take up any space in the aquarium and are hardly noticeable visually;
  • Various filter materials can be used as required;
  • External filters are often larger and can therefore perform better or circulate more water volume;
  • They are also easier to clean, maintain and, in principle, directly accessible;
  • Inlet and outlet can be flexibly installed in the pool.

The disadvantages of internal filters:

  • External filters are often more expensive to buy;
  • External filters are considered louder because the pumping noise is not dampened by the water and is often higher due to the power;
  • The sucker must be shielded to prevent fish from getting inside;
  • If the aspirator draws air, the technology could be damaged as well as the water quality.

For which aquarium internal filters are suitable:

  • Due to their high performance, external filters are mainly used from medium to large tanks
  • They are suitable for nano tanks as reduced versions that have to provide little power but hardly take up any space

Combine aquarium filters

In most aquariums, a filter system is completely sufficient. Above a certain volume of water, however, a higher filter capacity is required. But the demand for quiet systems also makes the combination of different filters quite interesting. Floor filters are often combined with small external filters. On the one hand, the microorganisms in the soil substrate can be optimally used, on the other hand, the external filter ensures enough water movement in the pool and covers the filter requirement.

The so-called Hamburg mat filter is also often integrated in the long term, preferably as a design element. For example, the roller-like design of the filter can be used both as a limitation and elevation, as well as a basis for moss surfaces and thus a breeding ground for microorganisms. Mat filters work purely biologically and are therefore very low-maintenance. In “calm waters” they are optimal, but often require the support of a small external filter.

For filter combinations, however, sand filters have also proven themselves, which are placed in the form of an extra tank under the actual aquarium. The water from the brimming aquarium flows into the lower tank via an overflow, where it is filtered through several layers of sand and pumped back. This gentle type of filtering is suitable for both freshwater and seawater aquariums.

The counterpart to the sand filter would be the trickle filter, which is attached above the actual aquarium, which is quite complex. The water is pumped up and, after passing through the filter materials, trickles down again like rain. The water surface moves only slightly, the lower regions remain still.

Such combinations of gentle filter methods are particularly recommended for numerous ornamental fish, since they prefer standing waters such as large lakes and swamp areas due to their origin. The same applies to shrimp, mussels, snails and crustaceans. Only a few species of fish feel comfortable in slightly stronger currents.

It is therefore important to consider which fish are to be used in order to find the right filter type or the right combination. It is also important to pay attention to the vegetation. Loose floating plants, for example, should also not be exposed to strong currents.

Maintain and maintain filters

Depending on the filter type, maintenance and repairs are more or less complex. Whereby modern devices have clearly gained in comfort and are very accommodating for the experienced aquarist.

For example, external filters usually have easily accessible filter materials that can be replaced as needed. Many internal filters rely on biological concepts for which hardly any maintenance is required. In any case, it is important not to underestimate the effect of accumulated microorganisms. New filter material always means the new build-up of the filter bacteria, and until then tighter control of the water quality until the values have leveled off again.

The filter is therefore often only checked during a complete water change and cleaned if necessary or repaired if there are problems with the technology. Ideally, the filter takes on the role of the breeding ground for microorganisms, which in turn do the filtration. Nevertheless, people must be able to retrofit or at least help out if necessary.

Natural and chemical support for filters

If, for example, the nitrate values ​​are too low or the nitrogen content too high, either because the filter is still virgin to bacteria or other factors have caused fluctuations in the sensitive balance of the aquarium, help is needed.

This can happen naturally:

  • by special aquatic plants;
  • in the form of filter bacteria that are already cultivated on the material or are added directly to the water.

Or by means of chemical additives:

  • through the use of activated carbon
  • through the use of black peat

Each filter material works differently. The electric filter pumps not only have the task of catching floating particles and creating some turbulence in the underwater world. Almost even more important are the microorganisms and chemical processes involved in filtration. Plants convert nitrogen into oxygen, activated carbon filters out odors and colourants, peat releases humic acid and fulvic acid and thus lowers pH and carbonate hardness, bacteria convert nitrite into nitrate, and so on. Only the complete filter system including internal or external filter, plants, microorganisms, additives and partial water change ensures a species-appropriate water quality in which fish and co. can feel comfortable.

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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