Keitech, isn't your tank the 2 week old with the 13 damsels? How are the other fish doing? If the cowfish is going into that tank, you really might want to consider slowing down with the livestock . . .
Yes, cowfish are potentially poisonous to the whole tank, if stressed or threatened. (This from Marine Fishes, not from experience.) In a cycling tank the fish do get stressed . . .maybe think about returning him? They are awfully cute, I know--but It would be a tragedy to suffer a whole tank wipeout.
tank with 29-gallon sump
2x Maxijet powerheads
Mag drive 9 return
Coralife 4x65 Lunar Aqualight
120 lbs rock from liverocks.com
1 peppermint shrimp and 1 fire shrimp (very shy)
2 black Ocellaris, Squish and Smudge
3 chromis, too identical to name as yet, in QT
29-gallon with two goldies, Carrot and Orangehead