Activated Carbon Use

OB Guy

Activated Carbon Use

One of the most commonly used chemical filtration methods is Activated Carbon.

There are a variety of pollutants dissolved in any aquatic environment containing biological life. Dissolved ORGANIC compounds (DOC's) include proteins, amino acids, phenolic compounds, pheromones and other metabolic byproducts which are continuously being exhausted into the aquarium water by the fish or other aquatic animals.

If these organic substances are allowed to become concentrated, they will negatively impact fish feeding rates, growth rates and reproduction rates, they will lower immune system activity and promote blooms of pathogenic bacteria in the water.

These DOC's can be controlled by water changes, however a pretty rigorous maintainance schedule is required. I recommend maintaining your nitrate levels at less than 10 ppm since doing so will concurrently facilitate a low level of DOC's, something which you cannot test for. The problem is that a great many aquarists don't adhere to such a maintenance schedule and don't test for nitrates.

If you are not managing your nitrates and thus your DOC levels, chemical filtration is perhaps the best method for you. Carbon filtering removes DOC's via adsorption. As the aquarium water flows through the carbon medium, the Dissolved Organic Compounds come into contact with the surfaces of the carbon granules where they become attached. this is ADsorption --- not ABsorption. Some DOC's are adsorbed directly, whereas others combine chemically with already-captured substances. When the surfaces of the carbon become saturated, it stops working and needs to be replaced with new carbon.

Thus, carbon does exhaust over time and needs to be replaced regularly. The effectiveness of activated carbon includes:

1. Adsorption: static forces that attract particles to the carbon which allows the particles to be consumed by Bacteria that settle on the carbons surface.

2. Diffusion of gases: This process includes particles absorbed into the carbon that are turned into gases and detoxified (02 into 03).

3. Chemosorption: Particles are irreversibly bound to the carbon it self.

So how much carbon should be used? Research suggests that generally, there needs to be 4 to 10 grams of granular activated carbon (GAC) for every gallon of water depending on stocking density.

Look for activated carbon which is phosphate free. A great many carbon grades are washed with phosphoric acid in an effort to support the adsorption sites since this is cheaper than degassing. This phosphate will leach into your aquarium water and can reult in a major algae problem.

Carbon absorbs most aquarium medications, especially antibiotics. Carbon should be removed while medicating so don't forget to put it back in when tank treatment is finished.

Carbon can deplete some trace elements needed for plants to grow. It should still be used to adsorb organics but only on a montlhy basis and only for 5-7 days.

If your filter uses prepackaged cartridges containing carbon, realize that these cartridges typically contain poor quality carbon and if quality carbon is used, only 20 percent or less of the recommended amounts of GAC is present. You can slit open the cartridge and fill them with more GAC but many pad filter types simply will not hold that much. Thus, the carbon in the vast majority of filter pads on the market simply is not functioning.

In a filter, the GAC should always be placed after the mechanical filtering medium otherwise, the particulates in the water will quickly coat the surfaces of the GAC, rendering it useless.

So what's the bottom line? If you're going to use activated carbon, you've got to use QUALITY material, you've got use ENOUGH of it to work and you've got to CHANGE IT often enough to keep it functional.

OB Guy

I used activated carbon years ago but now I only use it if I'm removing medicine from a aquarium.