I was readiong about these today but decided against them.
I think you can only keep one to a tank because they will fight. They may nip at corals and they release toxins into the water when attacked which can kill other tankmates. They also do this when they are stressed. Thats one of the reasons i decided against them.
from what i remember when they puff up they release tetradatoxin, true? into the water which kills all the tank mates. ive seen them get on with small fish like gobies etc at the lfs but yeah i wouldnt risk it, i think its the same with puffer fish? im not sure never read about them releasing their toxin into the water
We saw some boxfish at our lfs yesterday...the wife wanted one, but I warned against it. When they get stressed, they release a potent toxin. In the ocean, that's fine coz it gets diluted, but in the confines of the aquarium, it can easily kill everything. Best kept with peaceful, non agressive fish. They may also peck at any corals you have in the tank...