Jeff that is a really cool refugium. Did you build it? I like the way it looks. I understand completely that some people disagree with the deep sand beds. I personaly have never had a problem with them. On the what does it add to your tank question. This is again only my opinion. I believe they add over 20,000,000 nitrafying and denitrafying bacteria per pound. The aragonite dissolves at ph 8.2 and adds trace elements that the corals need to grow. They provide a place for spagetti worms to proliferate which breed and feed the corals. They in my mind provide for more area for life to exist. If you plan on keeping SPS corals they may not be the best idea. If your going to keep LPS or softies I think a deep sand bed is the way to go. On the flip side of the coin. Here is a photo of a SPS, Clam, Anemone tank up and running for many many years with a 55 gallon DSB refugium plumbed in line. It is thriving, has a very high fish load and is consistantly stable and healthy. I have a hard time beliving that sand beds are the terrible monster that sometimes they are made out to be. I think that sometimes they are givin the blame for other problems, because the results of other problems are seen in the sand bed first. Just my opinions.
