Poor fella, looks as if he has lymphocystis on his tail fin..
It's not fatal, has potential to lower their life span, but the virus itself has never killed a fish.
The virus that causes Lymphocystis infects fish fin and skin cells and causes them to enlarge significantly. At the outset of the infection, the infected cells may appear as white pinpricks - very similar to ich and other such diseases, thus making proper diagnosis difficult. However, as time goes on, these cells may enlarge and/or clump together to form nodules, lesions or lumps that can be larger than two millimeters in diameter. At the end part of this stage - which usually occurs in about the fourth week of infection - the engorged cells burst and the material inside them is released into the aquarium water. Which at that point you will want to do a 100% water change, and using hot water, clean out the substrate and decorations.
Salt won't really do anything.. but if treatment is done correctly, won't harm anything either. (You have gotten some great advice, and if you feel comfortable then I would say go ahead and follow it just in case there may be an infection.)
You will want to keep the water very clean while the virus is still doing it's thing.. in the 2 gallon bowl (2 gallons is plenty for a betta, just make sure to have proper heat), in the 2 gallon bowl you will want to be doing weekly 2 50% and 1 100%- the extra 50% is to make sure the water is kept cleaner during the process... keep an eye on it so when it bursts (think similar to a pimple), you can remove him as quickly as possible and do a 100% water change, etc.
Good luck.. keep us updated.
Last edited by Myates; 02-04-2012 at 09:31 AM.