We had a 16" naso in a 400g tank at the lfs as a store mascot he was with the owner for over 15 years. He made that tank look small, very active fish. Id say no on the 180 for the big guy. I have a 180 also and have been tempted to get a naso (my favorite sw fish) when I set it up, but I know its not really big enough and I would not want to rehome it.