I had Velvet, it killed all the fish in my frag tank - Yellow Tang, Red Scooter Blenny, Yellow Coris and Flame Angel.
I waited 3 weeks then got more fish - Scopas Tang, Melanarous Wrasse, Molly Miller and half a dozen Cromis.
All was fine for a week or so then I could see the outbreak happening, tiny spots with what looked like rotting flesh/fins.
I added a Schotling Oxidator and filled it with 6% Hydrogen Peroxide. I also installed a small UV unit and fed heavily. oh and I added a OF Hydra Filter as I suspected my water quality might be what triggered the onset of the Velvet (new frag tank using Marco rock) in the first place.
Now its about 3 weeks since starting the H2O2 Reactor and all fish are clear of velvet and they're really happy now, my tang doesn't fret when I put my hands in the tank, before she would have a fit every time.