eyrie, I do not ever trust 'cure-all' medications like melafix or bettafix.
Quote Bettatalk.com
"Immediately do a full water change. Keep his water very clean, changing it every third day. After putting him in clean water, add the antibiotic Ampicilex (Aquatronics) to his water. This medication comes in capsules. A full capsule treats 10 gal of water. So for a 1/2 gallon of water, open the capsule and take the right proportion of powder and sprinkle on jar water. You may steer gently with a disposable plastic spoon. This is a white powder and will not affect the color of the water. Do not overmedicate! Once Betta’s eyes are back to normal, stop the medication"
You need an anti-botic, not a cure-all. Ampicilex is what they suggest, maybe Kanacyn or Marcacyn are more popular and easy to find. Remember, get a specific anti-biotic medicine. There is NO such thing as a cure-all.