JC, the triggers are generally solitary fish in their native habitats so combining them in a small area even in a large tank such as a 210 may create problems. As I'm sure you are aware the clown trigger can be an extremely aggressive fish, at 3 inches he's small now but down the road very likely will become a problem. A few years ago I had a niger, pink tail and clown in a 155 for more than a year. At one point they started to attack everything, started with the clown first and then began to eat my coral so they had to go. Give it a shot but realize this may not work and you may need to take him back.
Scott