Can you post a vid of your tank? I'll be the first to admit that there was one time that I chose my tank based on what I liked as you mentioned above, but we should really plan our tanks based on what will be comfortable for our fish. They are the ones that have to spend 24/7 in there, not us...
Not bashing you, or anything, because your tank is beautiful, and the fish look healthy, but tangs are swimmers, not floaters like the marine betta. I have a 55 and 75 that I use for QT and HT when needed. I feel guilty right now watching my new PBT pace back and forth aimlessly in those 4 foot tanks. The gallon guides that we use to go by before we purchase livestock are a good rule of thumb, but honestly the way that the tank is made carries allot of priority as well. I'm upgrading to a 6 ft 225g right now, from my 5 ft 120g to support the size of my growing livestock. My yellow tank is only 4 inches long, and darts back and forth quickly, so I can only imagine how it'll be when he gets larger. Even with my 225g, there are certain fish I won't buy because of my limitations.
Best of luck with your tank...