LOL, looks like he might be in a crapper soon. There coloration pattern changes or get lighter/fades away secondary to neon tetra disease and there swimming is erratic. I had 10 neons in a 60 gallon and slowly one by one started to die. So, you got to remove the sick one and put them in differently tanks immediately which you did. The disease is caused by a sporozoan and I don't think there is a definitive treatment for it.
For the swim bladder disease, the belly get's pretty big (I had thought mine neons were pregnant at the time) probably to poor water quality.
In other words, I have a hard time keeping neon.