A couple years ago i saw a picture of a 20,000 reef tank. It didn't look much like a reef but it had great potential.
It was circular with an island in the middle, like a doughnut. Two bridges crossed over to the island. On the island was a closet to hold the scuba gear
It just had a few boulders in it and was way underlit
But that would be the ultimate
Unfortunately my wife won't let me convert our swimming pool to a 44,000 gal reef tank grrrr