The Mote Aquarium pharonis tank is quite a bit bigger: cylindrical, maybe 5-6' diameter and 4-5' tall. They have a number of animals in there, but they appeared to use most of the space swimming around. Of course, they have an open seawater system, so that doesn't have any bearing on the water quality requirements.
I'm not sure how big Paradox's single officinalis tank was, but that might give a rough estimate, since they're similar in size to pharonis.