Move the fish to a seperate QT, leave tank fishless for 4-6 weeks. DON'T treat the main tank and don't waste your money on anything but a copper based medication. None of those "Reef" safe or "Organic" ich cures have been proven to work. Act fast as velvet spreads quickly.
Some good reading:
http://atj.net.au/marineaquaria/amyloodinium.html