There's an ongoing debate about bettas and melafix, not sure if it has been resolved. This post is 9 years old but still informative:endlercollector said:I can't tell from the photo what the cause of the swelling might be. A good all-purpose medication is . I don't know if you can get it in your area. They don't sell it where I live, so I had to get it online.
Rtessy said:Yeah, better not use melafix. Are the scales turning white? Is that the only symptom? If so, I literally just dealt with the exact same thing, I'll post a pic and you can see if it looks similar (I had a more advanced stage though, if it is the same). I first tried kanaplex, which is a great medication, but it had no effect. I then tried a methylene blue dip of 10 drops in 1/2 gallon for 30 minutes, and the next day color started to return.
(Discoloration around the base of the dorsal which spread up the fin, and somehow jumped to the face).
If it looks nothing like this, please disregard... but kanaplex has worked well for me for a few issues, so it's a good go to.