I'm confused as to what this tank would look like? When you say rockless, do you mean no rocks of any kind, or just an artificial structure made out of something like concrete or plastic in an exact shape that you want? Without something to put the corals on, wouldn't this just be a glass box with a bunch of corals sitting on the bottom?

I didn't want to ask, but ya, what he said :)

Lol. I use tile for the bottom of tank and thought it might also work to build a structure out of tile.

oooooh, that could look so cool. Depending on the tile, you might not really be losing all that much filtration capacity. Unless it's polished it would likely still have tons of surface area on a microscopic scale.

You could build some really neat structures that way I bet.

That's what I'm thinking and being a shallow nano there not alot of scaping options.

I would use travertine tile