Which aquarium filter is the right one?

Anyone wondering which filter is truly suitable for their aquarium and inhabitants quickly realizes: there's no one-size-fits-all answer. A 30-liter shrimp tank has different requirements than a 240-liter community aquarium or a heavily stocked cichlid tank. The decisive factors are not only the liter volume, but also the animal stock, planting, maintenance effort, and the space around the tank.

The filter is not a minor issue in daily life. It moves water, retains dirt, and provides space for bacteria that break down ammonium and nitrite. A filter that is too small or unsuitable often leads to cloudy water, unstable values, or unnecessarily high maintenance. A model that is too strong, on the other hand, can cause more disturbance than benefit, especially in small tanks or with calm fish species.

Which Filter for Your Aquarium? First, Assess the Tank Situation

Before discussing specific filter types, it's worth taking a sober look at the tank. The most important question is not just how big the aquarium is, but how it is operated. A densely planted aquascape with few fish usually requires different flow and dirt removal than a tank with larger fish, a lot of food input, and correspondingly more pollution.

The shape of the aquarium also plays a role. In tall tanks, the flow must be guided differently than in shallow panoramic or room-divider aquariums. In open tanks, the aesthetics of the equipment weigh more heavily. For base cabinets or custom-made systems, it is relevant whether an external filter can be neatly accommodated and how easily maintenance remains accessible.

When choosing a filter, you should therefore always consider these points together: tank volume, stocking density, plant quantity, desired flow, space in or on the aquarium, and your own maintenance rhythm. Those who only look at the manufacturer's stated liters often buy too small.

Internal Filters - Suitable for Small and Simple Setups

Internal filters are the classic solution for smaller aquariums and the most obvious starting point for many beginners. They sit directly in the tank, are quick to install, and can be operated without additional hose routing. This is particularly practical for nano aquariums, breeding tanks, or compact complete sets.

The big advantage lies in their ease of use. An internal filter is usually inexpensive, immediately ready for use, and easy to monitor during operation. If the flow rate decreases, you quickly notice it. For tanks with low to medium stocking, this is often perfectly sufficient.

However, there are clear limitations. Internal filters take up space in the aquarium and are not always the most aesthetically pleasing solution. The filter volume is smaller than with many external filters, which leads to more frequent cleaning in heavily stocked tanks. In carefully designed aquascapes or display aquariums, the visible equipment block is also often a hindrance.

For small community tanks, shrimp aquariums, or aquariums up to about 60 liters, an internal filter is nevertheless often the most sensible choice - especially when simple maintenance is more important than maximum technical reserve.

External Filters - More Volume, More Quiet, More Reserves

As the aquarium gets larger, the question of an external filter almost automatically arises. These devices are located outside the tank, usually in the base cabinet, and pump water through multiple filter media via hoses. This creates more biological filter volume and keeps the equipment out of sight.

For medium to large aquariums, this is often the cleanest solution. External filters offer more reserves for higher stocking, can be equipped more flexibly, and are barely visible in the tank itself. Anyone operating a 120-, 180- or 240-liter aquarium will find this more convenient in many cases than a classic internal filter.

However, the advantage comes at a price. External filters are more expensive to purchase and require space outside the aquarium. Commissioning is a bit more complex, and maintenance is not done in two minutes either. However, they usually need to be cleaned less often. Clean hose routing and a secure stand are important, especially in households where the aquarium is present in the living area.

For heavily stocked tanks, larger community aquariums, or systems requiring a neat appearance, external filters are often the best choice in practice.

Hamburg Mat Filter - Underestimated, but Very Practical

The Hamburg Mat Filter, or HMF for short, is often associated with breeding or technical tanks, but it is also a very solid solution for many aquarists in everyday life. The principle is simple: water is drawn through a large filter mat, on which plenty of beneficial bacteria settle.

Its strength lies in biological stability. An HMF operates quietly, requires little maintenance, and is very well suited for shrimp, fry, or more sensitive stock. Because the flow is rather gentle, it is more pleasant in many natural setups than an overly powerful standard filter.

The disadvantage lies mainly in the aesthetics and the space requirement. A filter mat in the tank needs to be intentionally integrated into the design. In design-oriented aquascapes or very openly designed tanks, this is not for everyone. However, for those who prioritize function over show, the HMF provides a reliable and cost-effective solution.

Which Filter is Suitable for Your Aquarium Size and Stock?

For small aquariums up to about 30 liters, it is most important that the flow is not too strong. Shrimp, small rasboras, or Betta species rarely like constant current. Here, compact internal filters, air-driven sponge filters, or a small HMF are often more suitable than an oversized device with a lot of pressure.

In the range of 54 to 112 liters, much depends on the stock. A normally stocked community tank with plants often runs well with a decent internal filter. If you value an unobstructed view in the tank or want a bit more safety reserve, a small external filter is often the more elegant solution.

From about 120 liters, many practical reasons speak for an external filter. This is especially true if the tank is heavily stocked, larger fish are kept, or maintenance intervals should not be too short. Even for custom or panoramic aquariums with a clear aesthetic, external filter technology is often the more harmonious choice.

For cichlids, goldfish, or generally heavily polluting species, you should not plan too sparingly. Here, it is less the pure tank size that is decisive than the actual dirt input. A filter that theoretically fits on the box can still be too small in practice.

Look at the Flow Rate - But Not Blindly

Many people first look at the circulation rate per hour. This is useful, but only part of the truth. A high liters-per-hour figure sounds good, but says little about how much usable filter material is in the device and how stably the system works under load.

As a rough guideline: the tank water should be moved several times per hour, depending on the stock and layout. For gently stocked planted aquariums, less is often sufficient; for more heavily loaded aquariums, more is better. Too much current can stress fish, move plants unfavorably, and drive out CO2 faster. Too little current creates dead zones where detritus accumulates.

More important than the maximum pump capacity is therefore the combination of actual flow rate, filter volume, and sensible flow guidance in the tank.

Filter Media and Maintenance - Where Convenience Separates from Annoyance

Not every filter is equally pleasant in everyday life. Some models are quickly opened and cleaned, while others are robust but are rarely maintained due to cumbersome procedures. This is precisely when the typical problems often begin.

For biological filtration, sufficient colonizable surface area is important. Fine foams, ceramic media, or mats have their place here. At the same time, a filter should also retain coarse dirt without immediately clogging. A good balance saves work.

It is important not to clean the filter too thoroughly. Those who rinse all media under hot water or replace them completely deprive the aquarium of some of its bacterial culture. Gentle cleaning with aquarium water is better, and only when the performance actually decreases.

Which Solution is Usually Sensible for Beginners?

For beginners, an ideal filter is one that runs reliably, requires no complicated setup, and is easy to understand in case of a fault. In small tanks, this is often a solid internal filter. In medium-sized aquariums, stepping up to an external filter is often worthwhile if there is space in the base cabinet.

Those who mainly keep shrimp, care for young fish, or desire very gentle filtration should seriously consider an HMF or a finely secured sponge filter. For classic community tanks, the decision is usually simple: small equals internal filter, large equals external filter - with exceptions depending on stocking and design goals.

A practice-oriented specialist shop like Terboven Aquaristik is particularly useful when not only the filter itself needs to fit, but the entire system of tank dimensions, technology, and setup needs to be planned harmoniously.

Anyone who is unsure which filter for their aquarium to choose should therefore not opt for the strongest model, but for the most suitable one. A filter must work with the tank, not against it - and that is precisely what later makes the difference between constant adjustments and an aquarium that runs quietly and reliably.