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Using Activated Carbon in Your Fish Tank Filter

Using Activated Carbon in Your Fish Tank Filter

Updated on July 21, 2023
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Reviewed by Don Spaeth
Petco’s National Aquatic Care, Education and Programs Manager
Activated Carbon

Being the sixth most abundant element commonly associated with graphite, pencils, and the creation of diamonds, carbon is utilized in countless items that encompass our daily lives, one of which is an absorbing product for aquariums. This critical component of aquatic filtration has been used by generations of aquatic hobbyists.

Natural lignite and bituminous coal have been used in the creation of activated carbon for decades but products such as wood, peat, and coconut shells are also employed as well. Creating activated carbon utilizes a process which involves heating these items at extremely high temperatures which increases the overall surface area, removes impurities, and creates tiny pores. The surface area and tiny pores makes the active carbon highly absorbent, which is needed to remove dissolved contaminants from water.

What Activated Carbon Does in the Aquarium

One of the most common uses for carbon is prefiltering tap water. Activated carbon is very effective for removing chlorine and chloramine from municipal water supplies. Carbon is also effective at extracting phenols and tannins, components that typically contribute to the yellowing or browning of water from the aquarium.

Carbon does not absorb all compounds though- three inorganic compounds that carbon will not remove are nitrates, nitrites, and ammonia. Those must be removed through water changes or other chemical filtration additives.  Additionally, one downfall to carbon is that it is not selective, so along with contaminants, activated carbon will also remove some trace elements from the water.  Conducting regular water changes however, will readily replace trace elements that are removed.

Another application for activated carbon is removing medications. Because of its effectiveness, carbon should be removed from the filter prior to administering any medications. However, after completing the treatment and water change, utilizing fresh carbon will help remove any remaining medication that may be present in your aquarium.

Adding Activated Carbon to Your Filter

When adding activated carbon to your aquarium, some people may ask if they can just place a bag of carbon in their aquarium.  Remember, location is everything! Because activated carbon is porous, these pores can easily become impacted with debris, losing its ability to absorb the contaminants it was intended for. Carbon should be placed behind mechanical filtration within your filter because although a bag of carbon in your aquarium may absorb some contaminants, it will not be nearly as effective as it would if water was being forced through it within a filter compartment. 

Imagitarium Activated Carbon Pellets

Activated Carbon Maintenance & Replacements

Anyone that has ever touched activated carbon knows how dusty it is. This dust can be harmful to your aquatic life if not rinsed thoroughly. New carbon should be rinsed until the dust has diminished and the water runs clear. Rinsing activated carbon with prefiltered or distilled water will prevent it from absorbing chlorine and chloramine prior to being placed into the filter, thereby expanding its absorption capability.

Activated carbon has a phenomenal absorption rate but does not last forever. Eventually those tiny pores will have attracted and bound with as much contaminates as it can hold, becoming saturated. Typically activated carbon is effective for one month. If there is a heavy bioload in the aquarium or if it is used to remove medications, you may need to change the carbon more frequently.  Putting your aquarium on a regular maintenance schedule which includes water changes and carbon replacement in addition to rinsing or replacing your mechanical filter cartridge will help provide an environment in which your aquatic life will thrive and have you seeing clearly!

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