I wrote this in another thread, but every time digitates (and most colonial hydroids for that matter) are described in a post, someone inevitably suggests they might be able to sting corals because of their effect on seahorses. Personally, I wouldn't worry about it- if you go searching, while this theoretical tidbit is often repeated, I was unable to find a single reference on this forum or RC to anyone actually experiencing any coral damage from these guys. At this point, I assume they're perfectly safe in a reef tank and most will go away on their own in time.
