My lfs has a strange saltwater pond inside... lol. It is atleast 2000 gallons and has stone walls. It has an open to so people can touch the water (not that that's ok though). It has a waterfall too. There were two rays in there last time that were very social. They swam at the surface against the walls in a circle, and their bodies were waving, and when they passed us they had almost half of their disk thing out of the water. And they looked like they were smiling. Lol. I thought I had it on video but I can't find it. They also have a monster overflow system, but its hard to describe. Next time I go I will try to take some pics.