For a 45 gal.......DEFINITELY!
I had to get rid of my baby tang as they are constantly on the move & will be the hogs for food, if you have smaller fish that will have to compete.
They grow fast & deserve more room.
Be advised that they eat A LOT & crap even more, which can affect your water quality.
You can get small tangs now, but if you don't plan on up-grading tank size in the future..........I wouldn't do it.
Believe me, they are pretty & I wish I could too.
The Kole tangs are one of the smaller tangs & would be a better choice.