I've decided to list some sites that are clear with their ways of identifying diseases and how they go about treating/curing them.  So, check these out and see if they will help with your situation.  If you can't find a solution to your betta disease problem, I suggest you end their pain & suffering by euthanasia.  The way to do this is either to give them an overdose of anesthetics (if you have any) or just to put them into a plastic bag w/their water and put them in the freezer, where they'll go to sleep quietly...

Aquatronics Homepage: Disease Diagnosis

Faith's Betta Talk

Betty Splendens

For some quick steps for some diseases look below:

1.  Ick or Ich-Use anything w/Malchite Green and raise temp to 83.

2.  Fin Rot-(depends on stage though but...)Melafix with aquarium salt (1 Tbsp./5gal).

3.  Lameness/mal-nutrition due to poor water-use Betta Max!!!

4.  Non-Meds methods-Salt Method: Add 1 tsp. Aq. salt to 1 gal. of water for 3 days. (Total at the end of 3 days will we 1 Tbsp./1 gal. water. (usually works just about on any disease; fish are fine)

*I recommend to use Colloidal Silver (@GNC) for nutrition supplements during disease*