Melafix and pimafix is no good on what your fish has.Melafix is only good on cuts and wounds.You can add melafix with bacterial meds.The fish has already got secondary infections and fish are hard to save when this happens, so no melafix.
Ok, thank you. After isolating the beta, are there any steps that I should take to help the main tank? Or simply watch for symptoms later?
When you say "hard to save," is this fish actually dying from this? It has had the spot for a few months, and I have yet to notice any behavioral changes. If yes, estimated life-expectancy (currently 2 years old)?