Activated carbon is a great tool for aquarists. As with every tool, it's good to know how and when to use it. In this article, I will explain what activated carbon is for, when and how to use it, as well as enumerate its limitations.

What is activated carbon?

Activated carbon, in the aquarium hobby is used as a chemical filtration that removes dissolved organic compounds that are polluting your aquarium.

Most filter brands offer their own brand of carbon that fits into their filter. Some filters rely on specific cartridges that offer mechanical and chemical filtration.  You can also find it in bulk, where you refill your own media bags.

When should you use activated carbon?

Colored water

We don't want our water to be colourful; we want it to be clear! Yellow water often appears in an aquarium because of the presence of wood in the tank. Wood releases tannins, which make the water yellow. The carbon absorbs these tannins and helps clear up your tank.

As a precaution, boil the wood before putting it in your tank (let it cool down first, obviously). Boiling will remove some of the tannins. Change the water and repeat until you're satisfied with the result or you're simply fed up of boiling wood and need the pot to boil your spaghetti.

Some flake foods will tint the water if you're feeding too much and aren't making enough regular water changes. The activated carbon will help with the color of the water but you should also consider changing your maintenance and feeding routine.

If your aquarium water is white, carbon usually isn't the answer. White water is a more complex problem that I talk about in the article below :
Also read : How to Fix Cloudy White Aquarium Water.

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Odors

Even with a great maintenance schedule, odours happen. A dead fish, rotting foods, fish waste build-up, all of these can contribute to a hard-to-kill odour in our tank.
Activated carbon will clean that right up!

Medication

Activated carbon removes medications in your aquarium. Use it wisely.
When you start the treatment, remove your activated carbon.

If you used antibiotics, you're going to want to put a new activated carbon cartridge in your aquarium to remove it, once the treatment is done. Leaving the medication in your aquarium can have long term negative effects on your fish's kidneys.

Contaminants


The term "contaminants" is vague. It refers to anything in the aquarium that shouldn't be there.
Keep in mind that water absorbs what is in the air around it. If you smoke in the room where you put your aquarium, it will affect your water quality and fish health.
Activated carbon will help clear up that "second hand smoke".

If you have kids, I suggest always using an activated carbon. It makes sense to us that gummy bears don't go in the aquarium but that logic is lost on children, especially if they are not accustomed to the aquarium yet.
If ever dirty toys or sweet foods end up in your tank, at least your activated carbon is there to help!

Where should you place it?

Beneficial bacteria doesn't proliferate in your carbon cartridge. To avoid it getting clogged up with gunk, place it after your mechanical filtration, such as your sponge and ceramics.

How often should you change it?

The frequency at which you should change your carbon cartridge changes depending on the brand as well as on the amount of matter you wish to absorb.

As a general rule of thumb, most carbons will last about 1 month, unless specified otherwise on the bottle.
This being said, every aquarium is different. If your tank is over stocked or you have extra to absorb, such a medication, you might have to change it after 2-3 weeks.

Limitations

Activated carbon is great to have in your aquarium artillery but it still has its limitations.

Activated carbon won't remove ammonia, nitrite or nitrate, therefore it doesn't remove the need for regular tank maintenance.

If you have ammonia problems in your aquarium, there are cartridges that mix carbon and zeo-lite, an ammonia removing resign. Hagen's products that offer this are labelled as ZeoCarb.
ZeoCarb is a life saver if you're having ammonia problems. For more information on how to fix these problems, check out this article :
Understanding the Nitrogen Cycle

Activated Carbon cannot be rinsed or recharged. Once the pores are clogged, it won't absorb any more. Some people try and recharge it in their oven but, even though the over is hot, it's not nearly hot enough to reactivate this product.

Some brands of carbon have been found to leech phosphates into the aquarium, stressing out the fish and making it hard to control algae.
If this is the case, simply change carbon brands and add some Phosphate absorbing resign to help fix the damage.

Also read :
How to fix cloudy white aquarium water
How to prepare your aquarium for a winter power outage

Conclusion

Despite its limitations, activated carbon is a great tool for keeping your aquarium water clear and your fish healthy. Combined with good maintenance habits, you will be able to keep your fish happy for a long time.

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