looks to be right, either way they both will require a 180g or so at a size of 4 inches. they tend to be more active as they start to grow, they scavange for food, and at this period in the life of the fish, its best to have very high nutrition and plenty of growing space.
Ive always been a "big fish, small tank" guy... but I was going to say... this is a little bit overboard. Its not a unicorn tang... but your right, that species (whatever the common name) will get a lump on its head. They are pretty cool. Shouldnt get to be as big as a unicorn... but sizable and active none the less.