There are some products that you can find in every store that sells aquarium supplies and that every aquarist has purchased at some point or another, no matter how long they’ve been in the hobby or what type of aquarium they’ve had. Out of those stand-bys, how many of them do you really need, and do you know what they do (or do not) do for your aquarium? One of the most wide-spread of these “necessities” is activated carbon.
Activated carbon goes by many different names within the trade. “Activated” is sometimes interchanged with “active” and “carbon” is sometimes interchanged with “charcoal”. Any of these combinations generally refers to the same thing. The carbon comes from plant matter, generally hard materials like wood, nuts, coconut shells, bamboo or similar sources. The material is burnt in an oxygen-free environment until all that is left is pure carbon and some ash. At this point, the carbon produced is similar to the charcoal used as fuel and in your home grill although the charcoal sold as fuel is less pure than the carbon used in filtration. The carbon at this point goes through another process to “activate” it. During activation, the carbon is treated with hot gases like carbon dioxide, oxygen, or pure steam. Some activated carbon may also be produced chemically, wherein the material being made into the activated carbon is treated with a chemical first before being heated and the activation happens while the material is being “carbonized”.
Once the carbon is made into Activated Carbon, it is more suitable for use as a filtration media. Activating the carbon makes the pores in it larger so impurities “stick” to it better. Activated carbon is an adsorbent media; instead of soaking up impurities like a sponge, they stick to the carbon like a strip of flypaper. The impurities get trapped in the pores within the carbon itself. As a filtration media, activated carbon is used in many other ways other than in aquariums. It has medical applications, is used in drinking water or distillation filtration, in personnel protective gear, in air filtration and more.
In your aquarium, activated carbon is used to remove dissolved organic impurities, chemicals and other types of particles from the water. Different types and brands of activated carbon have different pore sizes that will target different sizes of molecules. They can range from smaller molecules like iodine to larger molecules like some dyes and medications. It can help remove odors (that fishy smell) and yellowish discoloration from the water from fish wastes, organic matter and material known as tannins from some woods and other matter (tannin is what makes your morning cup of tea look brown). It generally does not remove nitrogenous compounds like ammonia, nitrite or nitrate and does not eliminate the need for water changes. While effective in freshwater aquariums, activated carbon can remove some essential minerals like iodine and calcium and can cause the levels to be too low to support some corals and invertebrates. Activated carbon will become “full” and stop working over time, depending on how much work its doing in the aquarium and generally needs replaced at least once a month.
Will an aquarium function without carbon? Probably. Will carbon help the aquarium? Maybe. It is important to look at your aquarium as an individual system rather than fall into the trap of “It’s on the shelf and I’ve heard of it, so I must need it”. Like anything else, it has its uses (like getting rid of medications after treatment is done) and it has its disadvantages (like using up all the iodine that your crustaceans need to molt properly). Activated carbon is a traditional media for at least most freshwater aquariums, but if you aren’t certain if it is right for you, feel free to ask what your options are!