Puffers will normally make quick work of eating all crustaceans in the tank.That being said, I do have a small 4" porcupine puffer in my reef tank. On occasion, he will bite snails, but does not yet have the strength to break the shell, so no harm done. Leaves my hermits and cleaner shrimp alone, and my mithrax crab continues to make appearances. I also have a CBS that chases the puffer all around the tank, and will grab hold of the puffer's spines if it can. Not sure why, but it is quite comical when you think about it. The CBS did lose an arm, and I suspect the puffer may have tired of the harassment, but I don't know for sure. The CBS has regenerated the arm, and continues to go after the puffer.
I would say that my experience so far is the exception, rather than the rule, and am prepared to transfer the puffer to another tank when things change (it will outgrow the current tank anyway). ANd I am sure at some point, things will change.
The other problem with puffers is a water quality one. Puffers are large fish, eat a lot of food, and in turn, create a lot of waste. Not exactly what you want in a reef.
Just my 2 cents.
