I use activated carbon in two BRS reactors... 1 cup in each, for about 1 week at a time... i would never not use it, and i strongly recommend its use in a proper method, ie canisters fed with a pump... what i really like about the BRS reactors is you can actually exchange the smaller in diameter and crappy tubing they give you and set it up with... i replaced mine with 1/2" pvc and feed it with a mag drive pump... the only down side to any reactors imo, is the discs used to keep the media in place, usually gets clogged before the media is exhausted lol... but i believe very strongly in the use of activated carbon, which is always to be rinsed with fresh water before use...