carbon isn't used as a supplement, carbon is used on tanks to absorb organic and other chemical compounds. in a reef system it can remove both beneficial and detrimental things. some people never run carbon, some run it 24/7 I personally run it once a month for one week before a large water change. there are a couple different ways to run it. you can use carbon granules in a HOB filter, or in a bag in a high flow area of the tank, or if you have a sump you can run it in a media beg under the drop down or before the return, about the only wrong way to run it would be to dump it into the tank and leave it.