The freshwater aquarium filter: types and maintenance.

Over the years on Acquaportal, we have often talked about filters, filtration and filtration materials. The filter is always the heart of the aquarium and it is necessary to understand it well so that it can work at its best. 

 freshwater aquarium filter

The first distinction to be made to identify the various types of filters are:

  • mechanical filter
  • biological filter

1.1 Maintenance of a mechanical filter

1.2 Notes on mechanical filtration

The mechanical filter

The mechanical action filter mainly takes care of simply removing dirt particles, such as plant residues, uneaten food, and manure.

Generally, the flow of water flows quickly and the collected parts are treated by sponges or persons which will be rinsed often.

This type of filter usually has one or a maximum of 2 types of filter materials: sponges and hair.

When different materials are present, they usually have a different ability to hold dirt.

Sponges can in fact have more or less small pores and therefore be able to retain dirt of different sizes: the sponge with the smallest pores should be placed close to the pump, while the others closest to the water inlet.

Perlon wool typically holds more coarsely and is usually the first filter material the water will pass through in the filter.

Maintenance of a mechanical filter

In mechanically operated filters, the filtering material tends to get dirty quickly and therefore needs to be cleaned often.

To clean it you must NOT use tap water, but it is better to use aquarium water: just, when changing the water, collect the water in a basin and use it to rinse the sponges and the person several times and then put it all back together.

Notes on mechanical filtration

Mechanical filtration is typical of small quarantine tanks or for the growth of fry, but it is not a complete filtration system as, both due to the speed of passage of the water and the lack of suitable supports, it does not allow settlement of nitrifying bacteria in it.

Biological filtration

The filters that are already set up in the aquariums that we find on sale are normally biologically active.

They can be internal or external filters and consist of various areas for the insertion of filtering materials which, crossed by the water, perform their function of purification from harmful substances.

The main difference between mechanical filtration and biological filtration is the presence, inside the filter, of an area containing a substrate for the settlement of nitrifying bacteria. This substrate is generally the last one before the pump, in a dark area and is made up of razor clams, bio balls or other special substrates.

Path of the water in the biological filter

The biological filter typically contains:

  • person
  • sponges
  • battery holder
  • pump

They are often sold with charcoal as well: it is NOT necessary. It should be used only in special cases, in case of pathologies and use of medicines and removed once its function is completed.

The water entering the filter must follow a path:

  1. it is cleaned of larger particles, such as food residues, leaves, etc. through the  person
  2. it is cleaned of the finest particles by several layers of sponges with pores of different sizes
  3. it passes in the area of ​​the razor clams (or similar) where the bacteria have settled
  4. through the  pump, it returns to the aquarium

A deepening of the action of bacteria has been addressed in these articles that I invite you to read:

  • Slow nitrogen cycle and biological filtration
  • Freshwater aquarium guide
  • The most common aquarium filters
  • Filtering in the aquarium

Maintenance of a biological filter

Since the first part of the materials performs a mechanical action inside the filter, these materials must be cleaned quite often, in order to prevent the filter from clogging and the water from no longer being able to circulate.

You don’t have to use tap water, but during a water change, use the water collected from the tub to rinse the sponges and then put them back in their place.

No need to do anything else!!

Rarely and usually after several years if the initial part of the filter is well structured, it is possible to notice some brown sludge in the area of ​​the razor clams: it is very normal and does not preclude the functionality of the filter.

If you want, you can clean the filter container, again with aquarium water, taking care to NEVER leave the razor clams in the air, but always immersed in the aquarium water and possibly in the dark.

The razor clams or any other support for the bacteria should NEVER be washed or rinsed: it would only mean throwing away most of the bacteria themselves and restarting the maturation of the aquarium, even if only partially.

Other interesting articles

  • Undergravel filter for fry
  • Maturation in the freshwater aquarium
  • Air filter for fry
  • Air filter
  • DIY external filter for aquariums
  • External tube filter
Elizabeth Canales is fond of marine life since childhood and got an aquarium as a gift from her father on her 6th birthday. Since then she started to take care of Coralia (her goldfish). Her love for fish made receive her B.S. in Marine Biology from the University of Washington and DVM from Delaware State University.

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