Thanks all, and thank Hydro for your support.
Hehe, it is a DSB, but I'm excited by it's potential. I suspect that the grain size and depth is going to allow for great calcium buffering as well as excellent nitrate export. (Not to mention my sand dwelling critters will be in heaven.)
The trade off, of course, is less water cloumn, but I'm not worried about that. Fish live horizontally, not vertically.