While there are many methods of treating Betta fish diseases, there is one easy way to do it.
You see most of the diseases that Betta fish have is due to one source: Water
So, the best way to treat the diseases is to do a 20%-30% water change, everyday, till the fish recovers.
I have done that to my Betta fish before. You see, my fish looked listless and was lying on the bed of the tank. It is a bad sign because that means that it could die at any time. I did a 30% water change for 3 days and today I saw that it is back, active, flaring and very much alive.
Try it out. It may help your fish too.
Of course, this is not a foolproof plan. Some fishes will still die in the end but this is one of the easiest and surest way to treat a fish’s disease.