Really the main reason any marine fish become suited for fish only tanks is cause they well eat coral...... the second reason is cause they get too big. Thus leaving you with limited choices, for stocking a 30 gal FO tank. except damsel fish and reef safe fish.
I would recommend an exotic pair of damsel fish, rather than get a fish that will soon outgrow that small tank. Get some rock and add some of the non reef safe inverts as well!!