Well, if you're deciding on either a plenum or DSB for sump, you may want to get a good understanding of how a DSB works it magic. I converted from a plenum in my 150 gallon display tank to a shallow sand bed in the display and a deep sand bed in the sump. In order to get the most out of your DSB, you need to make sure you get the detritus to the detrivores in your DSB. I have a 100 gallon lighted sump and keep a fish, rock, macro/micro algea, snails, and a lot of worms in there. I have no detectible nitrates with this set up, but I have some hair algea cropping up in a few places in my display. To be honest, I thought my plenum system was more efficient since nitrate is converted directly to nitrogen gas and we don't have a significant amount of nitrate converting back to ammonium ions like a DSB. This usually isn't a big problem in a DSB since the nitrogen will eventually gas out, but this can fuel more undesirable algea growth than you would experience with a plenum. I doubt you could go drastically wrong with either setup. If I had to do it over though, I'd go with a fine shallow sand bed in the display (1.5 - 2 inches) and a plenum in the sump.
