What is activated carbon, and what does it do?

Activated carbon is essentially charcoal. That’s why you might hear it referred to as activated charcoal.

But what makes it so special is the way it has been treated…

Each piece of charcoal has been specifically manufactured so that it contains hundreds of tiny spores.

To put it very simply, these pores trap pollutants, making activated carbon excel as a chemical filter media.

Which pollutants exactly?

In aquariums, activated carbon is commonly used to remove…

• Chlorine and chloramines
• Tannins that discolor the water
• Phenols that cause bad smells
• Certain medications

You should already be using a good water conditioner for freshwater tanks or reverse osmosis (RO) water for saltwater tanks to remove chlorine or chloramines during water changes.

But where activated carbon really shines is clearing up your water and removing bad smells from your aquarium.

Activated carbon is so popular that most modern filters actually ship with a carbon filter already installed. Those that don’t have made room for you to add it yourself if you choose.

You should know that once the pores in the activated carbon fill up, they can no longer trap any more of these pollutants from your aquarium.

Because of this, you need to replace the activated carbon in your filter. I often do it during my regular maintenance routine. Fortunately, activated carbon is cheap, and replacing it can be done in seconds.

How long does activated carbon last?

Well, that answer entirely depends on how dirty your water is. The dirtier the water, the sooner you need to replace it. For a well-maintained aquarium, many fish keepers replace the activated carbon in their filter once each month.

To ensure the activated carbon in your filter lasts as long as possible, it should be placed after your mechanical filter. If you install the activated carbon before the mechanical filter, it will soon become clogged by the larger debris.

Oh, and don’t worry – activated carbon won’t leach any of the pollutants back into your water once it is full. While it is technically possible for activated carbon to release the pollutants, this would require some changes to the water chemistry that simply will not occur in your aquarium.^[3]

So, don’t worry if you forget to remove the carbon from your filter – it won’t harm your aquarium. Activated carbon is perfectly safe.

What can’t activated carbon do?

Activated carbon is often praised as this miracle product that will save your tank from any problems that may occur.

I hate to break it to you, but it isn’t true.

Activated carbon cannot remove the following:

• Ammonia
• Nitrites
• NitratesYou know, all the staff involved in the nitrogen cycle. Water changes and other methods must be used to remove these toxins.

Activated carbon also won’t remove heavy metals, such as iron. If your water source contains these, use a water conditioner before adding the water to your aquarium.

And of course, you cannot “recharge” or “reactivate” activated carbon. I have heard so many stories about how you can put activated charcoal in your oven to restore it to as good as new… Don’t waste your time!

You cannot rinse them either. Once the pores on your activated carbon are full of trapped pollutants, it’s only suitable for the trash.

I would also like to add that if you don’t keep your tank clean and perform regular maintenance, all the carbon in the world is not going to save your tank!