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Using Activated Carbon in Aquariums: How Long Does It Last?

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By Lindsey Stanton

carbon for aquariums

If you’ve ever experienced a stinky aquarium or have had difficulty getting your aquarium water clear, then you’ve likely wondered what you could do to fix those issues. The good news for you is that activated carbon is an excellent means of removing smells, toxins, and some water clarity issues.

Activated carbon is easy to use, relatively inexpensive, and widely available, making it an excellent choice for remedying your aquarium issues. Generally, activated carbon will last between 1 week to 2 months depending on the size of your tank, the output of your tank animals, and the chemicals in the water the carbon has been removing. Keep reading to learn what activated carbon is, how it works, and how long it will last in your aquarium.

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What is Activated Carbon?

You may have heard activated carbon being referred to as activated charcoal, which is essentially what it is. Don’t use regular charcoal in your aquarium, though! There are tons of activated carbon products on the market that are made specifically with aquarium safety in mind. Activated carbon can be made from peat, bamboo, wood, and more.

The most common and effective type of carbon used in aquariums is made from bituminous coal and is called granular activated carbon. To make activated carbon from these items, they are heat-treated at such a high temperature that it creates very small pores within the carbon. These pores increase the surface area of the carbon, which allows the carbon to draw impurities from the water.

Activated carbon is excellent at removing tannins, phenols, chlorine, and chloramines from the water. What this means for you is improved water clarity, less stinky aquarium smell, and healthier water for your fish. Activated carbon isn’t necessarily needed for a healthy tank, though, and many fish keepers do not use it at all. This strongly depends on preference and when it comes to using or not using activated carbon, there is no right or wrong answer.

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Considerations When Using Activated Carbon in Your Aquarium

There are two big considerations when it comes to using activated carbon in your aquarium. The first is that activated carbon can remove toxins and impurities from the water, but it will not remove ammonia or nitrites. This means that it won’t help reduce these levels within your tank and it won’t help cycle a new tank faster.

The second big consideration with activated carbon is that it is so effective at removing chemicals from the water that it will also remove medications. If you need to treat your tank with a medication, the instructions will likely tell you to ensure you remove any activated carbon from your filter. This is because the activated carbon will draw the medication from the water, reducing its efficacy significantly.

Once treatment is complete, most medications will recommend you then put carbon back into your filter to help remove any medication that is still in the tank.

How Long Does Activated Carbon Last in An Aquarium?

The answer to this question is technically that it depends. How quickly your carbon needs to be replaced will be based on the size of your tank, the output of your tank animals, and the chemicals in the water the carbon has been removing. If you placed new driftwood that released tannins into your tank, causing tea-colored water, then your carbon will absorb these tannins and be used up faster than it would be with clear water.

For a tank that is not overstocked and is using a HOB filter, then you’ll likely need to change the carbon filter cartridge every 2-4 weeks. If you are running an overstocked tank on a HOB filter, then you’ll likely need to replace your carbon every 1-2 weeks. For tanks with canister filters, activated carbon will need to be changed less often. Some fish keepers change out the carbon in canister filters every 1-2 months.

Keeping activated carbon in your tank longer will not necessarily harm anything, but it will lose its efficacy over time. If you do keep activated carbon in your tank past its usable life, then it may begin to colonize beneficial bacteria, which means you’ll be removing some of your good bacteria when you do finally change the carbon. Making a habit of changing activated carbon out on a regular basis will give you the biggest benefit.

Activated Carbon Options:
  • Filter cartridges: Filter cartridges are pre-made for specific filters, although some can be used interchangeably. These cartridges usually consist of filter floss filled with activated carbon and framed in plastic.
  • Loose activated carbon: Buying containers of loose activated carbon is usually the most cost-effective way to purchase activated carbon. You can purchase special aquarium bags made of mesh that you can then fill with loose carbon. This allows you to use however much or little carbon you feel is appropriate for your tank and reduces waste since you will be able to use the bag over and over.
  • Pre-filled bags: Some activated carbon is sold as loose carbon inside a pre-filled bag. These are similar to filter cartridges but lack the plastic framing that cartridges usually have.

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Activated carbon can be a beneficial addition to your tank if you perform the necessary upkeep. If you’re struggling with tannins, smells, or chloramines, or if you need to clean medication from your tank after treatment, then activated carbon can help you meet the needs of your aquarium.

Activated carbon is sold online and in pet and fish stores, and it is usually affordable. If you choose to use activated carbon in your tank, you can stop using it any time you need to. Some people use it in their filter all the time, while other people pull it after they feel the need has been met. What you do is up to you, just make sure to change it out regularly to maintain efficacy.

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Featured Image Credit: mdbildes, Shutterstock

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