dont know offhand, but whats the gph rating on those 2? I think the maxijet is like 175 or something? But i dont really see how you could fit a fuge and carbon in the hob..you'd have to run 2 seperate hob's imo. They're not that much anyways i dont think (the ac's). But you want the most surface area possible for your pods to grow in the sand, and carbon will cut that down quite a bit if you put it in there. Also, are you referring to just a bag of carbon, or the actual carbon pad things (where its a foamy/cotton/floss or whatever pad with carbon insided)? Because the pads would catch a lot of pods too which would kinda defeat the purpose of your fuge...the bag of carbon would be better, but still..its taking away sand space.
hth
mike