It sounds like velvet. (Dusty is a classic velvet symptonm. I'd google "marine Velvet" and see what you think. Velvet often looks like patches of velvety material, often goldish in color. Look at him with a flashlight from above, with the tank lights off, it becomes more obvious. Velvet is quick, very contagious and very deadly. If it is velvet, copper is the only cure I'm familiar with. A FW bath will give some temporary relief, but is not a cure. Basslets do not handle these parasitic diseases well, but you may pull him through. Again if it is velvet, all of your fish need to be treated with copper in a QT and the DT left fishless for 8 weeks or so. Was this fish new, in a QT, other new fish?