I would have to be a pretty big tank to be able to give up over 12" of vertical space. That would be over half of my 125 gal tank. In my refugium it would be nothing but sand. I can see Dan's reaction when I asked him to build me an acrylic refugium that could handle that much pressure without exploding.

I get the idea now. I guess that would be OK if it was a refugium dedicated as a sand bed. The other problem is that all the fine material generated by a DSB settles to the bottom. It would take a very fine screen to prevent that stuff from getting into the lower flow channel. You have the same problem with a plenum. I'd like to see one of these things. I guess I'm just throwing out a lot of what if's at this point, without seeing it in action.

Gary