So first off let me say that your tank is looking great and look forward to seeing it fill in soon! Second is a question about your rock wall.
I'm a big fan of the look and even made one myself before I relocated from Southern to northern California and sold the setup I was building. So I was wondering why you stopped the sand layer so far up from the bottom of the tank? I've seen a bunch of these in researching for building my own but don't remember having seen it stopped like that before.
Jeremy