Yeah....he's got Mycos. I'm so sorry. Myco's is not curable so what you are going to have to do is either let him go until he does pass or euthanize, there are a few humane ways to do this. The same goes for the Neon's, they might not show signs but if you put more fish in that tank you are infecting them instantly.
What you need to do is either let the tank run it's course and keep it completely separated from other tanks if you have them, equipment included or euthanize the Neon's as well so you can take the tank down completely. You can then spray everything with 91% rubbing alcohol from Wal-Mart, spray and soak everything. Then rinse it all out with tap water and let to dry out in the sun for a month. Or you can throw it all away and start over new, it's up to you. But that is literally the ONLY thing you can do to get rid of Myco's.