Its taking me a good while to type this answer for you, hope it helps.
And I pray that you are an extremely experience hobbyist and that you have a nice size large tank for its adult size. Do however keep this fish with very peaceful aquarium tank mates that will not cause any stress.
It feeds on all kinds of live and frozen foods. The boxfish also eats green stuffs and it would be best to feed small amounts several times a day. Also, generally feed squid, shrimp, and all kinds of chopped up fish. Be sure to wash these foods thoroughly before feeding, and you could go with a vegetable formula like Formula II. Other foods including worms, clams, various mussels, snails, tunicates, and fish. But never try any type of flake food for even that it could eat it, it wont be good for the fish long term
As an omnivore/herbivorous, its diet must be supplied with seaweed sheets or other vegetable preparations, and all foods must be fed below the aquarium surface, for floating foods may cause the fish to gulp air, thus causing potential problems with balance and buoyancy.
Like puffer fish, their teeth will continually grow throughout its life so you will need to supply their diet with some hard shelled foods. Occasionally foods like live ghost shrimp and various live snails will keep their teeth worn down.
Buddy