The Sohal shouldn't bother the clown as they're small. Sohal at that size, 3", aren't usually that aggressive but it will grow pretty quickly and then become a major problem in your tank.
Your tank, 180gal, is mostly to small for a 10"+ Sohal, which your will eventually become. Just be aware of this as a large Sohal will become a problem will keeping other tangs and some angel fish. So if you decide to add this fish make sure you take that into account as you'll a lot of people getting rid of one after it gets to large because of the problem it can bring.