Honestly, from the picture you provided I can't pick out anything physically wrong with your fish....I'm not really seeing anything white or fuzzy. Could you maybe try to get a couple more pictures of different angles? Maybe catch him in his cup/other small clear container if you can to get a better look at the area in question?
If it is some fungal-like infection, salt isn't going to do much on its own really. You'd want to QT him and start him on a round of some stronger medication...however, you don't do that until you're absolutely positive what you're dealing with....so a couple more pictures would be great if you can.
If you could please fill this out with as much information as you can, maybe even two separate ones for the 10 and the 1 gallon, that would be great.
Also, how is his 10 gallon decorated? Could you post a picture of the whole setup? And how did you acclimate him to his new home?