They need a large tank, they are considered an "expert only" fish due to being extremely difficult to get to eat. You need an established tank with lots of algae and they need sponges to eat. If you are not an expert, I would take it back. The tank size requirement, plus not being reef safe, plus being difficult to keep alive gives you all the reason to take it back without offending the wife. I bet she'd rather see you have a fish that lives and thrives.
If its going in your 150, then you are pushing the limits. 41 fish, some that will get huge, and adding another fairly large fish sure seems like a bad idea. I'm amazed that you have all those in a 150. I would think it was overstocked if it were a 300g.