so the crate goes under the rock to keep them just off the bottom?? To stack the rock up, are they just placed the rock together or have you glued them? I ahve found in the reef tank that the fish actually burrow in the sand so the under rock is exposed. My brown and white fish, two white strips,??? name??? :oops: love making caves, they work all day carrying sand out of their holes in there mouths, and then dump it over everything else!!