you could partition the 55 so that it's half sum, half refugium. It could be done with plate galss cut to fit or even acrylic / plexi-glass, they cut it to any dimension at Lowes and it's fairly reasonable. As far as lighting, most people run some sort of work light (clamp on types) with about a 6500k bulb (correct me if i'm wrong, but I'm sure I have read of others using that bulb). I have seen others use 48" shop lights. Setting up the refugium should be fairly inexpensive. I will be putting a couple of inches of sand in mine, but an not going to go crazy. I have seens pics of some with 6-7" of sand, it just seems like overkill to me. Hope this helps.