Activated carbon, also called activated charcoal or active carbon, is a processed form of carbon that works by adsorbing toxins, tannins (the stuff that causes the yellowing of the water), odors and organics in the water. Activated carbon can be made from many different materials, most commonly coal for aquarium use. It is available in a lot of different forms, shapes and sizes each having their own advantages and disadvantages.
Types of Activated Carbon:
- Bituminous: This is made from coal with a medium pore structure. It is soft, yet denser than lignite with a wide range of pore sizes. This makes it ideal for the removal of contaminants of many sizes and shapes. Bituminous is inexpensive, easy-to-use and hard enough that is doesn’t create too much dust. This is the most commonly used carbon for aquariums.
- Coconut: This is derived from the coconut tree and has a small pore structure. This activated carbon is both hard and dense, making it effective for the removal of small or high energy organic molecules.
- Lignite: With a large pore structure, this activated carbon is made from wood and peat. It is soft and light, therefore ideal for large or bulky organic molecules and other contaminants. Lignite is high performance, but it is more difficult to use since it takes longer to rinse due to the softness of the material.
How Granular Activated Carbon is Created:
- Pulverization: The base product, typically coal, is crushed into a fine powder.
- Agglomeration: The carbon powder is reagglomerated (ie reformed) into briquettes under several tons of pressure.
- Crushing: Briquettes are crushed to achieve the desired particle size.
- Baking: Baked at temperatures up to 800 degrees F to remove VOCs.
- Activation: Thermally-activated with exposure to temperatures up to 1900 degrees F. Activation is done within a controlled atmosphere using oxygen, stem, acid or salts.
- Screened / Sorted: Separated by size, shape and use.
What Are the Advantages of Using Carbon on Your Aquarium?
Carbon is very effective at improving overall water quality by removing a number of items, including:
- Contaminates: airborne solvents, some heavy metals, etc.
- Organics: portions of fish food, poop and other detritus
- Odors: odor-producing proteins and organics
- Toxins: chemical warfare between corals (particularly leather coral)
- Colors: tannins or yellowing pigments that block light and make corals appear more drab
What Are the Disadvantages of Using Carbon on Your Aquarium?
- Carbon adsorbs some beneficial elements, such as iodine, amino acids and medications.
- Although the science is still unproven, it could be a potential cause of head and lateral line disease (HLLE) for some fish.
- Carbon may release phosphate and other organics back into the water, particularly if it hasn’t been acid washed.
How Is Carbon Used?
- Media Reactor: A tube filled with media, which has water flowing through it at a desired rate.
- Media Bag: A porous, nylon bag filled with media and placed in an area of high flow (typically in the sump).
- Filter Sock: Simply added to a common filter sock, which then results in high water flow and pressure.
Common Forms of Activated Carbon Used In Reef Aquariums
- EAC (Extruded Activated Carbon): Minimal dust and can be made to develop specific pore structures.
- GAC (Granular Activated Carbon): The most common carbon in the aquarium trade.
- PAC (Powdered Activated Carbon): Compressed for use in aquariums. This is the base product used to make EAC.
Acid Washed vs Non-Acid Washed Carbon
Acid is often used to wash carbon to dissolve calcium carbonate, magnesium, salts, silica, iron nickel zinc, copper and other items. As a result, this creates more porosity for elements to be adsorbed when used. Generally, an acid-washed, activated carbon is more effective than unwashed carbon and less likely to release phosphates due to ash removal. Ash is residual, burnt up organics. Ash removal is important because it otherwise clogs the pores in the carbon, thereby reducing its effectiveness. For high quality carbons, an ash content of less than 0.1% is typical. Carbons with high ash content can cause a dramatic increase in pH. In contrast, acid-washed carbons with a lower ash content tend to reduce pH when initially used.
How Often Should Carbon Be Replaced?
Since bacteria will quickly take up residence in activated carbon, it is always best to change carbon out frequently. After a period of time, it will become coated in a biofilm that “clogs” the pores and renders the carbon useless. Fluidizing the carbon in a reactor will further help reduce the formation of this bacteria biofilm. Fluidizing is not recommended though, because it will create carbon dust that leads to issues for many reef inhabitants. As a general rule of thumb, we recommend running carbon for one week every month and replacing it with fresh carbon each time.
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