I guess its time for everyone to join in and have a belt or two.
Velvet (oodinium) is tough to diagnose at first; its easy once you've seen it. It always appears a little different; but a head-on look, in good light, will show a satin-like coating , often coppery color. It may cover most of the fish or just patches; fish with velvet are very still and breathing heavily. A FW dip can give temporary relief; but the ONLY (IMO & IME) cure is copper in a QT. I'd like to see you try to save these fish; but if this is velvet, they probably won't last the night. Velvet can be fairly quiet for a while, like in your tank, but when it explodes---its often a tank wipe-out. Velvet, IMO, is much more common than reported. I think many tank wipe-outs attributed to ich are really velvet and its a huge reason to use a QT with all new fish. If you Google (images) "marine velvet", you should be able to know for sure what you have.