Activated carbon for aquarium filter
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Activated carbon for aquarium filter

by Akua Design 12 Jan 2022

What is activated charcoal?

Activated carbon, in aquariums, is used as chemical filtration to absorb organic and chemical components dissolved in the water of your aquarium, such as odors, water or disease treatment drugs, contaminants, etc.

Charcoal is said to be active after having undergone various operations such as pyrolysis or controlled oxidation. These operations make it porous and thus increase its exchange surface with water.

In fresh water: Charcoal absorbs chelators because it has a great affinity for organic molecules, EDTA among others. As these chelators are bound to iron, we say in short, that activated carbon lowers the amount of iron available to plants.

In salt water: It is important to rinse it well under lukewarm or hot water before placing it in the decantation. It adsorbs terpenes and molting released by soft corals, organic molecules, possible drug residues, anything that colors the water yellowish, and many pollutants.

Which coal to choose?

Be careful to choose the brand used, almost all coals, even those that are very expensive, release unwanted phosphates! Some even release amazing amounts! As charcoal is rarely useful, and then only for short periods, a good solution is to place it in a small temporary filter.

Most filter brands offer their own brand of carbon that is the same size as their filter.

Some hang-on filters rely on carbon and foam filter cartridges, providing chemical and mechanical filtration at the same time.

Activated charcoal can also be purchased in bulk, where you fill your own reusable bags of charcoal with the desired amount.

In summary, for standard coals. If you want to use it, choose it well, do not leave it for more than 2 to 3 weeks and then throw it away. With the exception of AKUA DESIGN eco-charcoal, which is the only reusable and ecological charcoal on the market.

Why use activated charcoal?

Clarify water

We don't want our aquarium water to be dyed, we want it clear! The water becomes yellowish when there is wood in the aquarium. The wood releases tannins, which turn the water yellow/brown. Charcoal absorbs those tannins and helps you achieve your dream of the clear aquarium.

As a precaution, boil your piece of wood in water before adding it to your bin (letting it dry first of course). This action removes tannins and can even eradicate other biological components on your piece of wood that could contaminate your water.

Some flake foods can stain the water if you overfeed. Activated charcoal will remove the color but I strongly suggest changing your aquarium maintenance habits.

If your aquarium water is white, charcoal is not the answer. This is a much more complex problem.


Even with good maintenance habits, odors in the aquarium can happen; dead fish, rotting food, excess fish feces. All of these factors contribute to a smell that lasts. Proper maintenance of the filter with the addition of activated carbon in the filter solves this problem.


Activated charcoal removes drugs from your tray. Use it cautiously. When you start a treatment, remove the charcoal and put it back at the end of the treatment.

If you have used antibiotics, it is crucial to put the charcoal back on after the treatment is finished to remove this medication. If you leave the medication on for too long, there may be adverse effects on your fish and corals.


The term “contaminant” refers to anything in the aquarium that shouldn't be there.

Water absorbs everything in the surrounding air. If you smoke in the room where your aquarium is located, it will affect the quality of your water as well as the health of your fish. Activated charcoal will help you remove that sidestream-liquid-smoke (not to be confused with liquid-smoke for cooking, it doesn't taste the same).

Where to put the carbon in the filter or settlings

In fresh water: To prevent it from filling with sediment or other and reducing your water flow, place the cartridge after your mechanical filtration (sponges and ceramic) and in an area with a constant flow. Bacteria will grow and smother your charcoal if it is placed in an area with no flow or if it is not in your filter for too long.

In salt water: We advise in the marine aquarium to use reactors which allow a constant flow and which are easily installed in the settling filters, without having the problem of sticking with sedimentation.

We recommend once again to place our eco-charcoal, which does not need a reactor or specific filters. It can be placed directly in the decanter or standard filters without the risk of it sticking or clogging, since we have equipped it with a new format and honeycomb technology.


This “miracle” product still has its limits! Activated charcoal does not reduce ammonia, nitrite and nitrate. This product therefore does not remove the need to have a good maintenance routine as well as the need to properly cycle your aquarium before adding fish to it.


Despite its limitations, activated carbon is an indispensable tool for aquarists. It helps keep the water clear and our fish healthy. Combined with a good maintenance routine, you will be able to keep your fish healthy for many years.


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