Volitan: I heard that as well, but I saw an identical puffer in a 90 gallon reef at the pet store and it's been there for several months and hasn't nipped at any corals.
Umm...I used 60 pounds of caribsea aragonite for my sand bed. It is from 3.5" to 4.5". I dont have as much near the base of the live rock because i dont want crap getting stuck there.