roarsirroar, first, yeah, no Betta Fix or Melafix. It has an ingredient that can potentially harm a betta's labyrinth organ.
When you do the salt baths, are you leaving him in the water around the clock or are you putting him in the salt water for a short time and removing him? When treating with AQ salt, unless otherwise specified (for certain types of diseases/parasites), it's best to leave the fish in the salt water around the clock during the course of treatment. If you've been removing him after a short time, that could be why he hasn't improved.
If, however, you've been leaving him in the water on a 24/7 basis, then the salt obviously isn't working and it's time to treat him with Maracyn II. When treating with Maracyn II, be sure to keep him in a dim tank because it's a light sensitive medication and may not work as well in bright light.
It's not uncommon for bettas to lose scales but they grow back pretty fast. If he keeps losing scales though, I'd definitely recommend the medicine for sure.
Hope this helps you. If you ever need urgent help, PM me, DarkMoon17, or Oldfishlady.