Wet/dry Filter for Freshwater Aquarium

Last Updated on January 22, 2022 by Fabiola L.

Thinking of getting a new aquarium filter? Click and learn all about wet/dry filters for freshwater aquarium.

A large percentage of novice aquarists give up this hobby within the first two years. This mostly happens because they do not have enough time or motivation for regular (monthly) maintenance. However, with the right kind of setup, maintenance will never be a problem.

Continue reading to learn more about wet/dry filters for freshwater aquariums.

Why Is It Called Wet/Dry?

Wet dry filters are actually a specific type of trickle filter.

The name is appropriate because the water trickles down over the bio-balls, which are suspended in the air, thus they are dry. On the other hand, a mechanical or chemical filtration medium is usually immersed in water and accordingly is wet.

Thus, this filtration system has its dry and wet components, that is why it is so-called.

How Does It Work?

Wet/dry filter for freshwater aquarium work by trickling water through mechanical media to build up a good amount of oxygen before passing through the bacterial bed provided by bio-media.

Since bacteria need oxygen to process waste, they are considered the best biological filters you can find. Wet/dry filters usually offer 3 complete types of filtration, i.e., biological, mechanical, and chemical.

Three Most Common Configurations

  1. Bio-Media Sump Filters

Wet/dry filters using Bio-balls are great for use in heavily filled aquariums. They can also be used in freshwater and saltwater aquariums.

  1. Berlin Filtration System

The Berlin filtration system is predominantly designed for the saltwater reef tank.

  1. Refugiums

Use algae as well as live plants to consume and prevent the accumulation of nitrates and phosphates.

The combination of Berlin and Refugium proved to be the best choice for the whole and the best filtration.

The 2 Main Styles Of Wet/Dry Filters For Freshwater Aquariums

Filter Below The Tank

This is also the most popular style. Thus, wet/dry sumps are situated underneath the aquarium.

Water is drawn from the tank into the filter below, usually using a special overflow box. Once inside, it passes through a large tube down to the tank, where it passes through one or more barriers separating different areas of the filter.

As for the sump, it is usually about 1/3 the size (in gallons) of the main tank. Also, it can contain various aquarium filter media such as sponges, ceramic bio-rings, bio-balls, etc. Once purified, the water is then returned to the main tank using a pump located in the last sump chamber.

This type of wet/dry aquarium filtration is suitable for both freshwater and saltwater applications.


  • Suitable for freshwater or saltwater aquariums.
  • They allow the housing of sensitive fish species.
  • Greatly reduce tank maintenance.


  • You have to drill a tank if you don’t have an overflow box.
  • It is not aesthetically pleasing.

Filter Above The Tank

This is another, less popular type of wet/dry fish tank filter.

As for the process itself, the water is pumped from the submersible pump in the aquarium to the filter box in which the filter medium is located. It then rains over the media and returns back to the tank.

This type of wet/dry filtration is especially suitable for aquariums with Koi fish.


  • A very powerful form of biological filtration.
  • Allows the cultivation of aerial plants.
  • Returns highly oxygenated water.


  • Sometimes it is quite loud.
  • Requires the insertion of a pump and tubing in the main tank.
  • It is not aesthetically pleasing.

wet dry sumps

Five Benefits Of Using Wet Dry Aquarium Filtration

High efficiency

Did you know that it is on average two to ten times more effective than others? Wondering why? As you can guess, a more efficient conversion means a healthier tank.

When the filter medium is exposed to air and water at the same time, the bacteria convert ammonia into nitrate much better than when it is submerged.

Lower current

With this type of filter, bacteria work on oxygen in the air, not water. This means that high water flow rates are not required.

This is especially good because you will be able to avoid stressing fishes that have larger fins and a rounded body. Thus, low turnover rates mean less current.

Less Maintenance

Using this type of filter often means changing the water less often. Although it sounds impossible, you will probably have to change the water once a month. This monthly maintenance will be reduced to just sucking up the waste that accumulates at the bottom of the tank.

Suitable For Growing Plants

Wet dry fish tank filter allows aquaponics, ie, using fish waste to feed plants by pumping water to their roots.

Growing plants in aquariums that possess this form of filtration is especially popular because the process is twofold. It helps break down waste and use it for nutrients.

Did you know that many kinds of plants can grow at the top level of a trickle filter? It is only important that you provide your aquatic plants with a sufficient source of light.

Better Than Some Sponge Filters

The disadvantage of using sponges is that mechanical filtration is not separate from biological filtration. This most often results in the sponge being covered in debris that “suffocates” beneficial bacteria and reduces their effectiveness.

Also, you need to pay attention to nitrate reduction. Thus, the use of a sponge filter requires more frequent water changes.

To Wrap Things Up

Along with many different types of filtration methods, the wet/dry filter method is especially popular among aquarium hobbyists. They are excellent at converting ammonia to nitrites to nitrates. Also, wet/dry filters require very little maintenance, but you will still need to periodically clean the tubes and rinse the bio balls.

Have you ever tried using a wet/dry filter for a freshwater aquarium? If so, what were your results? Let us know your experiences in the section below.

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