I just got my Hagen AquaClear 200 for my soon-to-be planted tank. It came with two different kinds of media - a sponge and a sack full of carbon. I put the sponge in there already but not the carbon because wouldn't it filter out my ferts etc.? Are there any advantages to having carbon in a planted tank? I'm just wondering because my filter chamber is only 1/3 full, maybe I should add another sponge?