How does a carbon filter benefits an aquarium?Activated Carbon is amazing! The surface area is enormous and this allows bacteria to grow much faster and more dense. Just as we choose a porous rock for our grow beds (bio filters), activated carbon is an ideal surface for bacteria. It's not all good because activated carbon can also grow bad bacteria that is not beneficial to our systems, but with proper care, and aeration we can avoid many of these harmful bacteria
Depending on the ionization of the carbon it also has the ability to capture a lot of impurities. For example most activated carbon filters are very good at neutralizing chlorine.
Activated carbon filters will not remove microbes, salts or nitrites, but most organic chemicals have large molecules and due to the pore size of activated carbon many of the impurities we wish to avoid are converted in the activated carbon filter.
This is how it works in an aquarium, but in an aquaponic system the goal is to utilize as much grow space as possible. 3/4" media has been proven to work best. There are many choices of 3/4" media and I tend not to enjoy running my hands through crushed rock. I have found smooth rock works just fine. But recently there is a new idea being used called Bio-Char.