Bshane,
I had a 75 gallon SeaClear System II. That was also the type with the filter built into the back. Of course, that came loaded with Bio-Balls.
After my Live Rock cycled... and from learning about the hazards of Bio-Balls from this wonderful forum... I removed those Bio-Balls, 1/4 of them every week, for a month.
Having that spare room back there, I wanted to do something with it, so I converted it into a Fuge.
It works okay... but does have its drawbacks at the same time. Here is what I found:
being only 4" wide... any type of lighting you choose for your Fuge doesn't penetrate well. I had to turn my Chato weekly, or it had the tendency to die off underneath on me.
I didn't have an external sump with this setup. All of the circulation ran thru the Fuge area. This didn't seem to allow enough contact time with the Chato, for it to really grow, and remove the nutrients as I had hoped. YES, it was much better than NOT using this space, just not optimal.
Because all flow was running thru the fuge area, the Chato would almost act like a Filter Sock... collecting all types of decaying food deposits. On my weekly turn-overs... I would completely remove the Chato, shake it off in the water that I had removed for my weekly water change, to help remove these unwanted deposits. Because of this, I wasn't able to develop the POD haven that I had hopped for back there.
Once again... its is MUCH BETTER than NOT having a Fuge... those are just the drawbacks that I found when I had mine setup that way. Hope this info helps some.