oh here on bettafish.com has the info i used at one point.dont know if yo have checked it out or not..but its surely worth a try..
DISEASE: TAIL ROT OR FIN ROT (OR BOTH!)
This disease comes mainly from dirty water. If you keep his water VERY clean Mr. Betta will never get tail/fin rot. It is not overly contagious, and bettas will more than likely recover if treated promptly. Fins/tail will grow back, though may not have same color or may not look as good or be as long.
frayed fins and a darker edge are clear signs of fin rot
Betta’s fins and/or tail seem to be getting shorter and shorter. Or they seem to be falling apart and dissolving. There may be a darker color (or a reddish one) to the edge of the betta’s fins/tail. He may be still active and eating normally, or may have stopped eating, fins may be clumped, color may be pale.
Do a full jar water change. Use tetracycline or Ampicillin (included in our Betta First Aid Kit) combined with Fungus Eliminator (included in our Betta First Aid Kit). Change water every third day and add a new dose of same medication. Continue until fins/tail stop receding and start showing some new growth. This may take up to 4 weeks, so don’t give up. Once rot stops and fins start growing back you can stop treatment, but not before then.
Note: If the rot is very slight or mild, you could use Maracyn I and Maracyn II (together at half the dose each) by Mardel. These med can help but are not very powerful. They come in hard tablet which is a real pain to administer. You'll have to crush them into a powder before you can administer to a betta in a bowl. A tablet treats 10 gal of water, so you do the math. Do not overmedicate! If you are caught by surprise and do not have a First Aid Betta Kit (naughty naughty), then you can run to a local Petco or something and probably find the Maracyn I & II and at least try that. My advice though? Be ready! Get your Betta First Aid Kit now so you have the real powerful stuff at hand and are ready when the you-know-what hits the fan! (or life will get real messy LOL).