I've been talking about a new frag tank system all year. It's November and I'm finally getting it done. The frag tank was made a month ago, but I needed a stand. I'd considered a steel stand to match the rest of my setup, but the cost just didn't justify itself.
Back in November 2013, I set up the 400g anew after a very long wait for the aquarium to arrive. I got my rockwork just right, added my corals, adjusted the lighting period, and tended to my reef. My general rule is keep my hands out of the tank, something I tell people often.
Using carbon in your reef will help improve water clarity, which allows better light penetration for your corals to utilize. I've been using GAC in a reactor for years, and never had any problems. Perhaps because I follow the rule of thumb of using only 1/2 a cup of a carbon per 50g of water.