Activated carbon - how it works and how to use it

Probably the most commonly used chemical filter medium in reef tanks is activated carbon. With the help of activated carbon, many different compounds can be removed from the aquarium water. These include, for example, the so-called yellow matter, which are organic molecules (mainly fulvic and humic acids) that lead to an unpleasant yellow coloration of the water and that significantly reduce light penetration. In addition, activated carbon removes harmful nettle toxins that your corals continuously release into the water.

How activated carbon works: adsorption on a large surface area

Activated carbon is carbon that is processed into highly porous material. The manufacturing process creates an extremely enlarged inner surface. Adsorption describes the property of a medium to bind certain molecules to its surface. It occurs, for example, due to van der Waals forces or electrical charges (=ionic bonding). All chemical filter media have a certain maximum lifetime after which no further compounds or molecules can be adsorbed from the environment. Therefore, activated carbon must be renewed regularly.

Especially in aquariums with mixed stock (soft and stony corals) the use of activated carbon is beneficial. In addition to light-absorbing yellow substances, activated carbon also removes growth-inhibiting nettle toxins.

What should be considered when using activated carbon?

#1 Goal: Yellow matter removal for clearer water

Since the removal of yellow matter (e.g. humic acids) is accompanied by a change in the radiation intensity of the lighting (and thus with a light adjustment for corals), the first time the activated carbon should be used carefully and slowly. For example, start with 10 g per 100 liters of aquarium water and increase week by week until you have reached about 40 - 50 g of activated carbon per 100 liters of aquarium water. This amount is sufficient for continuous use. After 4-6 weeks the activated carbon should be renewed.

#2 Goal: Remove drugs or toxins

Toxins (e.g. after the death of a sea cucumber in the aquarium) and medications should be removed from the aquarium water as quickly as possible. Therefore, in such a case you can use a larger amount of activated carbon 100 g/100 liters). Ideally, the activated carbon should be placed in a media filter with a strong flow (200 L/h). In such cases, replace the activated carbon early, for example after 3 days, as the activated carbon can also release the toxins again when conditions change.

Activated carbon such as Tropic Marin Carbon should not be missing from the emergency kit of a well-stocked aquarium household. No matter whether you accidentally overdose trace elements, a poisonous animal dies in the tank or dinoflagellates spread. Using activated carbon makes sense in all cases to reduce the toxic effects.

#3 Goal: Remove ozone and clean exhaust or supply air

When using ozone, activated carbon should be installed downstream to remove excess (and potentially harmful) ozone from the water. In addition, for very large aquariums with a correspondingly large ozone input, we recommend connecting an activated carbon reactor for the exhaust air downstream of the skimmer to remove excess (and potentially harmful) ozone. The supply air of the skimmer can also be filtered with activated carbon. This is particularly useful in smoking households or where scented candles or similar are used intensively. The replacement intervals for the activated carbon are about 3-6 months for this use.

Washing activated carbon before use - yes or no and above all how?

There are different opinions on this topic:

1. Wash activated carbon with hot water and leave in it for a while
2. Wash activated carbon with osmosis water
3. Wash activated carbon with salt water

And what is the best choice now? We can recommend you to wash the activated carbon in the first place, because this removes the carbon abrasion, which would otherwise unnecessarily irritate the mucous membranes of your fish in the water and can also have a negative effect on some corals, such as xenia. Washing with salt water should prevent the formation of boundary layers. Washing with hot water is supposed to displace all air from the pore system of the activated carbon. Whether these 2 methods really improve the functioning of the activated carbon noticeably, we cannot say at this point in time. Washing the activated carbon at all is a good idea in any case.

Adverse effects of activated carbon

Activated carbon can also have adverse effects. In addition to pollutants, it also removes important trace elements and is suspected of causing lateral line disease (e.g. in tangs). Very intensive use (duration or quantity) should therefore be treated with caution and should be accompanied by close monitoring and, if necessary, adjustment of the trace element balance.