The deal on velvet...
"Because of its lifecycle, a general recommendation has been to quarantine new acquisitions for 20 days to avoid introducing the disease (Noga, 2000 and
Trevor-Jones, 2004), but I would urge most hobbyists to isolate them for a full month, with six weeks being optimal, for a number of reasons. The first reason is for uniformity. Because it will take at least a month to known if your new acquisition is free of
Cryptocaryon irritans, it is better to simply get used to a long period of quarantine. Second, the signs of this infection are not obvious and, in my opinion, most aquarists can easily miss them. A full month or more of quarantine should give you enough time to notice the infestation, or, if you don't pick up on the signs, the fish will likely be dead by the end of the quarantine period."
from
http://reefkeeping.com/issues/2004-0...ture/index.php