I looked them up here is an excerpt:
"The Blue Spotted Boxfish or Hawaiian Boxfish (Ostracion meleagris) is another favorite in the aquarium hobby. They grow only as large as 6 inches, so they can be easily kept in a smaller 55 gallon tank. ... they feed on algae, sponges and benthic invertebrates, including polychaete worms, small bivalves, tiny snails, and copepods. However, tunicates are considered to form the major portion of their diet. Their teeth are designed to scrape food, such as tunicates and sponges, off of hard substrate. These fish are active during the day when they hunt for food. At night, they rest by hovering above the substrate. Their care is is similar to the Longhorn cowfish, but they are much more difficult to keep. They easily succumb to a number of parasitic, fungal, and bacterial infections. It is best to keep live rock in the tank with this species.
Unfortunately, this species is the most well-known for toxin release. They are considered poor swimmers and must rely on toxic body slime and their tough body shell for protection. Toxic episodes occur more frequently when Blue boxfish are kept with more than one of their own kind. It is imperative that two males of this species NOT be kept together. Surely bickering will result in toxin release.
Blue boxfish appreciate plenty of swimming room and some caves or crevices to hide behind. Like the Yellow Spotted boxfish, they are also known to jump out of tanks. "
I would'nt advise keeping them in a 29 gallon tank.It also sounds like they would be very difficult to feed.
