If it is just this one fish, and quick cure didnt do anything, I would not think it was Velvet really since it spreads so quickly that your other fish would almost certainly have the same problem.
There are a couple of other things I might check into. The first would be "Head and Lateral Line Erosion" and/or "Hole in the Head" (Hexamita). These were my first 'inkling' when I saw the pictures, but then again, it is hard to see all that great, probrably because I dont have the best monitor in the world on this computer.
I would try the vitamin suppliment idea within the head and lateral line erosion description in either case. Feeding your fish a few thawed out frozen peas that you can gently squish will always be a good thing from time to time.
Otherwise, I would try an anti-fungal medicine. Otherwise I would suppliment the Melafix (which is more bacterial in nature as far as what it treats, but will also be great to help your fish heal) with Pimafix (which is more fungal and internal bacterial in nature as for what it treats) since the combo is reguarded by Drs. Foster & Smith as a "natural botanical remedy for fungal and bacterial infections" (
http://www.drsfostersmith.com/Produc...m?pcatid=11269) and may prove to be more 'all-encompasing' as far as you not knowing exactly what you are treating and helping to heal the fish. Otherwise, you can step out of the 'natural cures' and go with a more un-natural medicine, but be aware that some of them will also kill off your benificial bacteria colony and you would need to be prepared to deal with that by testing your water as if it was a brand new tank (mine seemed to bounce back very quickly though when I used antibiotics on a cynobacteria problem I had)
help! Sick guppy :( 
