I like the idea of a hang on the back fuge/skimmer but I am thinking it cant be good to hang 30-35 pounds of water on the back of a small tank. said:
Well personally, I would do it separately. I know cpr and other companies have the skimmers built in now, but the problem I see there is, the skimmer is pulling nutrients out of the water before the macro get a chance to get some of it (kinda defeats the point). On the other hand, I doubt the skimmers are that great, but I don't have any personal experience there.
I originally set my 40g w/o a fuge, but ended up using a HOB fuge from cpr, the med size one (I believe its ~19").
I don't know how much the fuge helped or if the system just became more stable over time, but I tend to feed heavy, and noticed that even with a medium stock of coral, and 5 smaller fish, my nitrates are always 0. However, I do run a skimmer (aqua C remora), and do ~7-10g water change every other week.
To decrease the wt/pressure on the back glass of the tank, I just use extra support that I cut to fit the distance from the wall to the fuge (a small piece of dowel rods w/ rubber on the ends) to help support the tank.