What Does Activated Carbon Do?
The use of activated carbon in marine tanks is considered to be a form of chemical filtration. Working through absorption, activated carbon removes gelbstoff (the compounds that give water in an aquarium the yellow tint), some large organic molecules, medications, chlorine, pollutants and toxins, as well as many other types of chemical elements and compounds from the water that a protein skimmer or another means of filtration may not remove.
Activated carbon can also remove the trace elements and minerals that are important to your fish, invertebrates, and corals.
A recent study has found that the heavy use of activated carbon in marine aquariums can cause Head & Lateral Line Erosion disease (most often seen on fish in the Surgeonfish Family). This can be avoided by using a trace element additive in the aquarium.
Because of its large surface area per volume, activated carbon also makes a good biological filtration platform.
Pelletized carbon is used in the DIY Carbon Tube Filter with excellent results. When activated carbon is placed in a Canister Filter, is also serves as a biological Filter.