Fin rot is usually caused by poor water quality, so have you thoroughly cleaned the tank? You should be doing lots of water changes as clean water is
very important to ensure a healthy environment during (and after!) your fish is healing. Do you have any other fish with fin rot? If so, they can cross contaminate each other if you're using the same things to clean the tank with or the same net.
I've heard good things about a product called "Jungle Fungus Eliminator" for advanced fin rot.
You have to keep on top of it, because fin rot can lead to body rot which you REALLY don't want to witness. If it's been a month with no change, I would try some different medications and keep that tank
clean. Or better yet, isolate him in a heated hospital tank in order to give the bacteria that's probably in his home tank a chance to die off.
There are lots and lots of great articles on the internet of fin rot, here are a couple to get you going:
http
/www.healthybetta.com/articles/Illne...sis/finrot.html
http
/www.bettatalk.com/betta_diseases.htm
Note: I'm no expert on the subject, so I heartily suggest doing your own research and asking lots of questions, hopefully some of the more experienced members can give you some more advice.
I wish you and your Betta the best of luck!
Edit: Whoops, I almost forgot to add, some medications work best at higher water temperatures. Is your tank heated?