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Filtration & Media


December 13, 2018 | By Tom Sarac

by Tom Sarac

Filter media is the core of what a filter does and how well it is going to actually filter aquarium water. The media content of your filter represents its filtration capacity. Simply put, your filter is the vessel that makes changing and maintaining filter media convenient, and it facilitates continuous and effective water flow through the media.

Your filter should be used to its full potential by ensuring its output is aggressively moving the surface of the water since this is how you increase the dissolved oxygen content in water.

Different filter media exist for varied purposes. For example, for removing an odour or improving water clarity, carbon would be your typical choice.

If your goal is to lower pH and create the type of tropical conditions where black water South American fish are found, peat granules are recommended.

For the health and survival of your fish you will want to ensure there is strong biological filtration present, and in this case you could use Fluval BioMax and/or Fluval Bio-Foam.

Water quality starts with effective biological filtration. The basic requirement is filter media that is porous and offers a large surface area. It is equally important to remember that nitrifying bacteria that provide this all-important aquatic function are aerobic (oxygen-loving bacteria), therefore, you want the filter output to move and break the water’s surface.

So, let’s consider the basic types of water filtration as well as the types of filter media best suited for the job.



This category of filtration is responsible for removing solid debris from your aquarium

It has a lot to do with keeping water clear and your aquarium clean. Fish, plants, and some natural decor all contribute some physical waste to your aquarium. Mechanical filtration takes care of trapping unwanted debris.

The most common and versatile mechanical filter media is foam. Cell size can vary in foam so accordingly so does the size of waste it removes. The smaller the cell size the finer the debris it can immediately remove. Foam also has good capacity, making it very capable of handling large waste loads. While foam can be rinsed and re-used many times to ensure its effectiveness, it is strongly recommended to replace it at least twice a year. As it ages in water, it becomes increasingly difficult to rinse thoroughly and may start to wear and break down.


This form of filtration occurs when various impurities are trapped on or in a chemical media, and includes ionic exchange where an unwanted ion is exchanged for a harmless one.

Carbon is the most common chemical filter media used in an aquarium. It effectively traps gases and various other dissolved impurities within its structure, including toxic metals such as copper. Not only does this result in crystal clear, odourless water but creates much purer water for fish.

Carbon is manufactured from an extremely important raw material that directly impacts water filtration capability. Fluval Carbon is made from bituminous coal – the best source material for carbon that is used for water filtration.

When it comes to getting the most from carbon, it is important to replace it regularly because bacteria will colonize it, debris will clog it, and as it saturates with impurities, there is risk of it leaching some back into the water. Think of carbon as a paper towel – its use is to clean something prior to being discarded.

It is strongly recommended to dispose of carbon monthly or immediately after it has effectively accomplished a specific requirement, such as the removal of medication after a treatment, clearing of an odour, cloudy water, etc.


This form of filtration occurs when natural living bacteria converts the biological waste created by fish and other organisms in an aquarium into a form other bacteria use and remove from the water.

The by-products of the biological waste are known as nitrogenous waste, which can be ultra toxic depending on the pH and concentration. The aerobic bacteria that perform this essential filtration prefer filter media in filters to colonize due to the dimmer or light-free conditions within. Also favourable to them is the strong supply of dissolved oxygen provided by the actual water flow through the filter.

Bio-media does clog over time, and it is recommended to provide clean filter media for effective colonization by bacteria. This family of nitrifying bacteria will benefit from partial media changes every 3-6 months to ensure clean porous surfaces are available. Regular cleaning and replacement of mechanical media, such as foam, also promote better conditions for the growth and prosperity of these beneficial bacteria.Remember, your aquarium filter will best support your aquarium when it is properly maintained. As we have pointed out above, filter media defines the capability of your filter. Just like the tools in the hands of a skilled mechanic, your filter is one of the most important tools for ensuring you have a well-tuned and healthy aquarium.


Aquatic expert Tom Sarac provides guidelines on knowing when to switch out the most common Fluval media for your aquarium filter.


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