Activated carbon is a porous form of carbon that can be used to absorb or remove dissolved organics that give water its yellow tint. Removing these materials will help with biological filtration and increase water clarity. In theory, better clarity will aid light transmission through the water column and improve PAR (Photsynthetically Available Radiation, which is all radiation between 400-700 nm wavelength range)
Does Activated Carbon Remove Beneficial Trace Elements?
One of the big arguments against using activated carbon on a continual basis is that it removes beneficial trace elements from the water. I have used carbon continuously on all of my tanks and have not seen any negative side effects on my corals. This is purely an observation and not based on any scientific facts. According to MORE