Marine velvet starts off looking like ich but with the fish breathing heavy. Velvet kills fish pretty fast and it's usually to late to save them by the time you realize what it is. Freshwater dips help and copper treatment in a QT gets rid of the velvet. If it is velvet, you have to QT and treat all the fish with a copper treatment and leave the display tank fish free for 8 weeks.
I have a link in my signature about my expirence with velvet, and I found this link
http://www.reefkeeping.com/issues/20...ture/index.php very helpful.