Can you post a pic of him? A fish with velvet looks something like this:
If he looks similar to that, then there is a good chance he has velvet. Otherwise, many fish naturally have a gold iridescence to them. With velvet, it looks like gold dusting but each speck is well-defined. In a serious case of velvet, you will even see the parasites on the eyeballs, like with my Gershwin in the pic (got him that way from Petco).
Velvet can be pretty hard to treat with chemicals because only one stage in the life cycle is susceptible to chemical treatment. Your best bet is with AQ salt, like you have begun doing. If you can, get him into a small tank, 1-2 gallons. Crank the heater up to about 86 F, gradually so you don't shock your fish. Add 3 tsps of AQ salt per gallon, predissolved in a little bit of tank water.
Now the fun but very important part. You need to do at least 50% water change every day and vacuum the bottom of the tank really well. This is what gets the nasty parasites out before they can reattach. I highly recommend doing 100% water changes as it makes redosing the salt a lot easier.
Also, keep the tank as dark as possible becaue velvet photosynthesizes. Some people even go so far as to shove it in a closet. o.O So drape a towel over it and keep it in the darkest room of your house.
Continue with the salt treatments until you no longer see any velvet parasites. Then do a 25% water change. Do not add salt. Next day do a 50% water change. Again, do not add salt. Finally, do a 100% change to get his water completely salt free.
I hope this helps you. Good luck!