Activated Carbon In An Aquarium – How Much, Benefits, & Uses

    Activated carbon in an aquarium

    Using activated carbon in an aquarium can be helpful, but if you’ve never used this material before, you may have wondered what it does and how it can benefit your fish.

    Activated carbon is a super porous and absorbent substance that can remove toxins in your aquarium water, including foul odors, discoloration, and chlorine. It can enhance water quality and clarity, which can help you maintain a healthy aquarium.

    If you’re interested in learning more about aquarium carbon, our in-depth guide will explain everything you need to know. Let’s get started!

    What Is Activated Carbon?

    Activated carbon or activated charcoal is a type of carbon that is used as chemical filtration in fish tanks to remove pollutants from the water. It can eliminate a wide variety of contaminants in your aquarium water, including tannins, chloramine, chlorine, and odors.

    Using activated carbon in your tank can greatly improve the quality and clarity of your water to keep it at optimum level.

    This video does a great job explaining the uses of activated carbon in a fish tank:

    YouTube player

    How Does Activated Carbon In An Aquarium Work?

    Activated carbon is made up of tiny pores that are highly absorbent which work to soak up organic and inorganic pollutants in your aquarium water. It excels at removing tannins, chlorine, chloramine, phenols (causes of bad smells), and heavy metals (copper, lead, nickel, etc).

    Unlike regular black carbon, activated carbon is filled with oxygen to expand the millions of tiny pores between the carbon atoms. Each layer and hole attracts and binds containments, including organic chemicals and certain inorganic compounds.

    Activated carbon isn’t just used in fishkeeping – it’s also used to purify gasses and liquids in drinking water, pollution control, food and drink processing, and more.

    Types Of Activated Carbon

    Activated carbon comes in a few different types, but not all of them are the best choice for aquarium use.

    The most common types of activated carbon are:

    • Granular activated carbon (GAC)
    • Bead-activated carbon (BAC)
    • Extruded activated carbon (EAC)
    • Powdered activated carbon (PAC)

    Ideally, you should be using granular activated carbon for your tank. 

    Powdered activated carbon can be dangerous if it is not housed in a media bag as it can get lodged inside your fish’s gills. Some aquarists have discovered carbon dust in their dead fish’s gills and fin tissues after close inspection.

    It’s best to use GAC or carbon that comes in large pellets to reduce the risk of this happening. Always make sure you rinse away ash, dust, and debris on carbon before you add it to your aquarium.

    What’s The Difference Between Carbon Black And Activated Carbon?

    Compared to carbon black, activated carbon has a larger surface area, so it is more effective at binding to compounds. In addition, carbon black is normally a fine powder, whereas activated carbon is typically granular.

    How Does Activated Carbon In An Aquarium Benefit Fish?

    Rainbow fish (Melanotaenia boessemani)

    Using activated carbon in your tank has a few advantages on your fish, including:

    • Clarifies aquarium water
    • Removes bad odors
    • Removes chlorine and chloramine

    Improves Water Clarity

    One of the first benefits of activated carbon in an aquarium is its ability to increase the clarity of your tank water. It does this by removing tannins, the latter of which can be caused by bogwood, decaying plant matter, and fish feces.

    While tannins from wood or Indian almond leaves can be beneficial to fish, discoloration due to rotting plants and organic waste can be harmful as both of these could lead to an ammonia spike or high nitrate levels.

    Using chemical filtration in your saltwater or freshwater aquarium adds another layer of polish to help you maintain good water quality.

    Removes Bad Smells

    Activated carbon in the aquarium can help remove phenols to rid your tank setup of bad odors or that dreaded “fishy” smell. Phenols are typically caused by the breakdown of live plants, fish poop, and uneaten food.

    Over time, phenols can build up to high levels and lead to lethargy in fish. In a saltwater aquarium, phenols can be particularly unpleasant as they can inhibit the growth of invertebrates.

    Although you’ll still need to perform regular tank maintenance, you won’t need to do it as frequently if you use carbon filter pads. Besides, your aquarium will smell considerably better!

    Removes Chlorine And Chloramine

    Activated carbon removes certain toxins like chlorine and chloramine, both of which are lethal to fish. Activated carbon is often used by aquarists who use RO (reverse osmosis) water in their tanks as it can assist with keeping the membranes intact.

    Some fishkeepers also use carbon instead of water conditioners to dechlorinate their tank water.

    Bear in mind that activated carbon does not remove ammonia, nitrite, or nitrate from aquarium water. Frequent water changes and a cycled tank are vital for keeping your fish healthy.

    Best Kinds Of Activated Carbon To Use In An Aquarium

    Best activated carbon for aquarium

    While there are numerous advantages of using activated carbon filtration in a fish tank, it can be difficult choosing the best kind for your setup. There are so many aquarium carbon products on the market, some of which may be poorly made and ineffective as a result.

    That’s why we’ve compiled a list of the best activated carbon media for a tank. They’ll have no trouble keeping your aquarium healthy and crystal clear!

    MarineLand Black Diamond Premium Activated Carbon

    MarineLand is well-respected in the aquarium hobby as they produce high-quality fish tank products, and the Black Diamond Premium Activated Carbon is no different.

    You get 22 ounces of high-quality activated carbon in the tub, so you should be set for several months. MarineLand’s activated carbon works well to remove discoloration, bad smells, and other organic compounds in your tank.

    Bear in mind that this is loose activated carbon, so you’ll need a mesh bag to put it in before you add it to your aquarium!

    Fluval Carbon Filter Media

    Another reputable brand you can rely on for your fish tank supplies is Fluval, so you can trust that Fluval Carbon Filter Media will keep your aquarium water sparkling clean. 

    The carbon used in each mesh bag (you get three in a pack) is low-ash and very porous, which provides a big surface area for rapid absorption of dissolved organics in your aquarium water.

    Better yet, Fluval Carbon Filter Media is free from phosphates and won’t alter your pH levels.

    Aquapapa Activated Carbon Charcoal Pellets

    If you have multiple fish tanks or simply want to stock up on activated charcoal for your aquarium, Aquapapa Activated Carbon Charcoal Pellets are a great option. You get six pounds of phosphate-free carbon and zipper mesh bags to fit it all inside.

    The carbon media bags are reusable, which saves you a bit of money in the long run. You could use them for other filter media too!

    AquaClear 70 Activated Carbon Inserts

    Suitable for freshwater and saltwater aquariums of up to 70 gallons, AquaClear 70 Activated Carbon Inserts are a solid choice if you need chemical filtration on a budget. There are three filter carbon inserts in a pack, so you should be good to go for a few months.

    The filter pads quickly absorb inorganic and organic substances to provide stable water chemistry and a clean aquarium. While these filter cartridges are made with AquaClear 70 aquarium filters in mind, they should be suitable for most filters that are of a similar size.

    If your filter system is a little small for these filter pads, you could always cut them open and move the granular activated carbon to a separate mesh bag.

    How To Clean Activated Carbon For Aquarium Use

    Before you use activated carbon in your aquarium, it’s a good idea to clean it to wash off dust or debris. The job of filter carbon is to remove pollutants, not to add to them!

    Step 1: Remove the carbon from its packaging and place it in a mesh bag (if it doesn’t already come with one).

    Step 2: Run warm dechlorinated water or old aquarium water over the carbon media bag to clean off any dirt. If your carbon is in pellet form, you may need to rinse it for a few minutes.

    Step 3: Once clean, place the activated carbons into your filter system (canister filters, power filters, etc), ideally after your mechanical filtration media.

    Don’t use tap water to wash new or used carbon as it can soak up the chlorine in your tap water. It’s also worth placing old carbon against your ear after you’ve rinsed it to check whether it is still activated.

    Activated carbon should produce a crackling sound when wet (the moisture helps the activation process). Carbon that is no longer effective will make no sound!

    How To Use Activated Carbon In An Aquarium

    How to use activated carbon in a fish tank

    As mentioned earlier, activated carbon is ideal for removing organic chemicals from your tank water, so it can be a great addition to your filtration system. But alongside boosting the filtration in your water, there are a few other uses of carbon in the aquarium.

    Increases Quality And Purity Of Your Water

    One of the main uses of activated carbon in a saltwater or freshwater aquarium is to increase the quality and purity of the water. Adding carbon to your aquarium filter will get rid of discoloration, bad smells, and other pollutants in your water.

    This helps you maintain a clean, healthy environment for your fish, as well as makes your water much clearer and less stinky. And that allows you to get more enjoyment out of your aquarium as you’ll be able to see your fish better (and smell them less!).

    Removes Aquarium Medication

    Carbon filtration is useful for removing medication from your aquarium water, especially if you accidentally dose too much or no longer need to medicate your fish. 

    However, this also means you need to remove carbon from your filtration system before you use any treatments in your tank water.

    Increases The Effectiveness Of Protein Skimmers

    Adding carbon to the aquarium can improve the effectiveness of protein skimmers by assisting with the removal of organic proteins. Protein skimmers aren’t usually necessary in a freshwater tank, but they can be very useful in a saltwater aquarium or an outdoor pond.

    They work by pumping tiny air bubbles into your water, which helps remove organic waste to keep your aquarium clean and free of surface film. When used alongside carbon, protein skimmers become more efficient.

    The activated carbon will assist with the removal of finer, less complex organics as the protein skimmer tackles the larger organics.

    How Much Activated Carbon To Use Per Gallon In An Aquarium

    Tank Size Amount Of Activated Carbon Needed
    10 Gallons 0.5 Cups
    20 Gallons 1 Cup
    40 Gallons 1.5 Cups
    50 Gallons 2 Cups
    75 Gallons 2.5 Cups
    100 Gallons 4 Cups
    150 Gallons 6 Cups

    Every aquarist has their own method when it comes to measuring out the amount of carbon needed in a tank, but this chart is a good starting point. 

    The amount of activated carbon you need in your tank depends on the number of organic/inorganic wastes in your tank, as well as the brand you use. Most aquarium activated carbon brands will list recommended dosage on the back of the packaging.

    How Long Does Activated Carbon Last In An Aquarium? 

    Guppy (Poecilia reticulata)

    Activated carbon doesn’t last forever – it will eventually become saturated and no longer able to absorb pollutants in your water. Aquarium carbon usually lasts for two to four weeks, so it will need to be replaced after this time.

    However, there are a few factors that can influence how long activated carbon lasts in a tank, including the number of pollutants in your tank, the quality of the carbon, and the placement of the carbon.

    High Number Of Contaminants

    If your tank contains a lot of pollutants, the carbon in your aquarium will become oversaturated pretty quickly. There is a limited amount of surface area for containments to attach to the carbon. 

    Once filled, aquarium carbons are no longer effective and will not provide any benefit to your tank setup.

    Low-Quality Activated Carbon

    Cheap or low-quality activated carbon will usually have a higher phosphate and ash content than high-quality carbon, as well as deactivate sooner. You can tell whether the carbon you use is of a good grade by looking at its ash content, molasses value, and iodine value.

    Poor Placement Of Carbon

    Carbon in the aquarium should be placed inside your aquarium filter after the mechanical filter. This allows it to purify the water as soon as it enters the filter while also helping it stay free of debris.

    Putting the carbon in the wrong place can cause dirt and grime to build up, leading to quicker deactivation and a lower absorption rate overall.

    How To Replace Activated Carbon In An Aquarium Filter

    Even the highest quality carbon will lose its effectiveness over time, so it’s important to know when and how to change it. Carbon usually needs to be changed every month, but it may need to be replaced sooner depending on how much carbon you use, its quality, and the number of pollutants in your aquarium.

    Bear in mind that cleaning activated carbon once it is deactivated won’t increase its effectiveness or reactivate it.

    Step 1: Remove the carbon filter cartridge or mesh bag containing your carbon from your aquarium. Don’t remove your biological filter media as that’s needed to grow beneficial bacteria!

    Step 2: Discard the filter pad or empty out the carbon from your mesh bag. Clean the new carbon under dechlorinated water or old tank water to wipe away excess dust and ash.

    Step 3: Place the new carbon back into your aquarium filter after the mechanical filter media. That’s it!

    How Is Activated Carbon Made?

    Activated carbon is made in several steps, which are all vital to the activation process. First, the raw material of the carbon (bituminous coal, coconut, peat, etc) is warmed up so it loses all of its moisture. The dry material is then ground until it is powder.

    The powder has a binding agent added to help it compress into a solid carbon block. The solid carbon block is then crushed up into small pieces and placed inside a kiln.

    Initially, the pieces are heated to 200 to 750° F to eradicate volatile organics. The heat is then increased to 1000° F until they become charred carbon pieces.

    Lastly, the carbon is doused in steam at 1800° F to expand its pores and surface area.

    Can You Make Activated Carbon For An Aquarium At Home?

    Molly fish (Poecilia latipinna)

    Yes, you can make activated carbon at home. However, the process can be both time-consuming and expensive. It’s much cheaper and more convenient to buy aquarium activated carbon online or from a fish store.

    That being said, if you’re interested in making carbon yourself or fancy a new DIY project, here are the supplies you need and how to do it:

    • Charcoal
    • Glass jar or a non-aluminum pot
    • Calcium chloride
    • Cheesecloth or a white sheet
    • Storage container
    • Water and a measuring cup
    • Cookie sheet

    Step 1: Create charcoal by burning coconut shells, hardwood, or bituminous coal in a heat-proof container. You may need to burn the materials for several hours depending on the size of your container.

    Step 2: Using a hammer or mortar and pestle, crush up the charcoal into a powder and place it in a glass or non-aluminum bowl.

    Step 3: Create a 25% solution of calcium chloride by diluting it with water. For 300ml of water, you’ll need 100g of calcium chloride.

    Step 4: Add the calcium chloride and water solution to the powder, then stir it with a spoon until a paste forms. Discard any excess solution.

    Step 5: Leave everything to dry for a minimum of 24 hours.

    Step 6: Grab some cheesecloth and spread the mixture onto it. Next, rinse the mixture with clean water and use a coffee filter to catch excess carbon that flows through.

    Step 7: Put the charcoal on a cookie sheet and bake it in the oven for 30 minutes at around 250F. The charcoal can be removed from the oven once there is no more moisture left.

    Step 8: Let the charcoal cool and break into small parts before placing it into an airtight container.


    Can activated carbon in an aquarium harm or kill fish? 

    Activated carbon will not hurt or kill your fish. However, it can increase the amount of phosphate in your tank, which can lead to algae growth and green water.

    In addition, if you use activated carbon that is of a subpar standard, it can cause your pH to rise. In some cases, the pH levels in your tank can skyrocket, which can be detrimental to the health of your fish.

    Does activated carbon affect pH in an aquarium?

    Yes, activated carbon can affect pH in an aquarium if it has a high ash content. Poor-quality carbon often contains a lot of ash, which can contribute to a rise in pH. It’s best to use acid-washed carbon as this process will remove the ash.

    Does activated carbon affect water hardness in an aquarium? 

    No, activated carbon will not affect the water hardness in an aquarium. Carbon only removes organic contaminants and specific inorganic compounds.

    What is activated carbon made of?

    Activated carbon is made of materials that are rich in carbon like coconut shells, lignite coal, wood, peat, and bamboo. The most common carbon source for carbon used in aquariums is bituminous coal, but coconut-based carbon is also fairly popular.


    Activated carbon in a fish tank
    Severum cichlid (Cichlasoma severum)

    Activated carbon has many uses in the aquarium, so it can be a real asset to your filtration system. It does an excellent job of removing tannins, phenols, chlorine, and chloramine, which helps keep your aquarium clean and healthy.

    However, activated carbon isn’t a necessity as long as you’re performing regular water changes and keeping an eye on your tank parameters. It’s ultimately up to you if you decide to use it or not!

    If you have a lot of organic chemicals in your tank or don’t enjoy the appearance of natural tannins in your water (like those caused by Indian almond leaves and driftwood), then activated carbon may be worth using.

    Alternatively, if your aquarium has a stinky smell or you need to remove medications ASAP, activated carbon can be very useful.

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