When I was Setting up my 180 I bought a bunch of sand from a guy who had sting ray tank!  Thing was like 500 gallons and not much rock.   It had sprig a leak and had to tear down,  I wasn't able to see it running but he showed me pics of it.  Can't remember his name but the Rays would eat from his hand like down town and made a nice water mess in his fish basement.    Do it mermaid be the first in the club!! Would be cool for sure!!