add a little bit of salt, proportional to the amount of water in the tank. I'd say every time you change 1 gallon of water from the tank, add 1/4 of a teaspoon of aquarium salt...just to be safe..
Melafix seems to be recommended throughout the web. ive never used the stuff (as i stay away from using any prepared meds) I hear that indian almond leaf has benefitial properties...its usually very cheap online...
also your betta should be in heated water with temps around 79-82F
treatments work best around that temp as well...