@knight; Lionfish is quite correct in what he is recommending for your 30. Any Dog or Pork will outgrow it in no time, but the Canthigaster group (valentini, fiji, sharpnose, and others) will do ok in a 30 for a long time. In my reference book it states "A 20-gallon plus, fish only aquaruim would make the best home for this species of fish".
Sidenote to Lionfish; You must be planning to come into money if you are getting a Golden Tonga Puffer lol.