DIY Kaldnes Media Aquarium Filter - A Step-By-Step Guide

What is Kaldnes Media?

Kaldnes media was designed and developed in Norway by the combined efforts of education, government and private sectors: the Norwegian University of Science (NTNU), the Foundation for Scientific and Industrial Research (SINTEF), and Kaldnes, a Norwegian industrial company. 

In the early 1980's, NTNU and SINTEF were developing sewage treatment technologies involving moving media. By the end of the 80's, the partnership had successfully developed a new method of treating wastewater called "the moving bed biofilm process". By this time, Kaldnes was getting involved, and plans to produce and market the technology were begun, with a newly formed company Kaldnes Miljøteknologi AS.

This new sewage treatment was intended only for municipal use, but other industries, such as aquaculture, quickly adopted the media and the process, now called the Kaldnes Moving Bed (KMB).

How Does Kaldnes Work?

Kaldnes media are small pellets made of polyethylene that look like wagon wheels. The media come in different sizes, but aquarists primarily use the K1, the smallest size measuring 1cm in diameter. As you can see, the plastic media have a lot of ridges and surface area for nitrifying bacteria to grow.

K1 Kaldness Media

K1 Kaldnes Media

Kaldnes vs. Traditional Ceramic Media

Ceramic media are the most common bio filter media used by aquarists. It looks similar to porous gravel or small pieces of lava rock. Kaldnes media is superior in a couple of important ways.

Kaldnes Media is:

  • Light with a density slightly lower than water so that it is buoyant. Ceramic media is heavy and dense by comparison.
  • A moving bed filter whereas ceramic media does not move once placed in a filter. 
  • Self-cleaning. Ceramic media needs to be cleaned regularly (although most aquarists don't).

Kaldnes media is used in a reactor which provides aeration and agitation. This mechanical movement of the media is the key to it's superior nitrifying ability (to break down ammonia to nitrite and then finally to nitrate). As the media moves in the reactor, it bumps into the reactor walls and other media, sloughing off excess biofilm, keeping the media clean so that nitrifying bacteria work at it's peak efficiency. Since ceramic does not move, the biofilm that covers the media gets clogged by "sludge" which is dead nitrifying bacteria and fish waste. Also, the tank water does not flow easily throughout ceramic media thus is far less efficient than Kaldnes media.

Constructing A Kaldnes Reactor

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Step One: Materials and Tools 


  • Power drill or a very sharp awl
  • Pencil or chopstick

Materials and tools to make Kaldness Media Filter
Materials and tools to make Kaldnes Media Filter

Check valve prevents floods during power failures
Check valve prevents floods during power failures

Side-drilled suction cup
Side-drilled suction cup, sometimes called pilot hole suction cups

Making openings in the water bottle

Use the drill to make starter holes in the water bottle lid and on the top and bottom of the bottle. Please refer to the video at the end of this blog. Use the pencil or chopstick to gently increase the size of the holes, careful not to damage the bottle.

Make a hole in the water bottle lid
Make a hole in the water bottle lid

Insert airline tubing into bottle lid hole
Insert airline tubing into bottle lid hole

Airstone attached to airline tubing
Airstone attached to airline tubing

Air stone inserted into bottle
Air stone inserted into bottle

Finished Kaldness Media Filter
Finished Kaldnes Media Filter,
just after installation.

Finished Kaldness Media Filter - 3 hours later
Finished Kaldnes Media Filter - 3 hours later

Full Video Instructions

The video below is a tutorial that provides real-time instructions on building the Kaldnes media filter. 

Kaldnes filter Set to the Music of Yo-Yo Ma

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