I mix rox carbon and brs gfo in a bag and stuff it in the bottom of my third chamber where water flows in from chamber 2. I change it every three weeks. Hope it works for you! Good luck.
That's the exact same stuff I got. I have it right where the water cascades from chamber 1 in to chamber 2. I have my HOB skimmer pipe in chamber 2, so it's keeping the bag right where the water cascades.
I'm hoping to see some improvement between that, and the water changes that I'll start implementing. I have been noticing that my water isn't crystal clear, so I'm sure the carbon will help out with that, and the GFO i'm really hoping will help my algae issue, and help the SPS finally take off in the right direction!