another newbie
I don't know much about fin rot but I can tell you what happened to my platies. I bought them and the male had a small amount of fin rot on his tail. took someone's advice and gave him a salt dip. He seemed to be doing well, healing and eating, active. Then I noticed the female had fin rot. Instead of giving her a salt dip, I added salt to the tank VERY SLOWLY over a week. The male died. The female was doing great and then died unexpectedly. I don't know if it's because they were platies. Check out some sites on fin rot. I've seen recommendations for putting hydrogen peroxide directly on the fins and letting is dry for 30 seconds. I don't know about that. There are medications too but I've never used them. I'm sure there are members that know a LOT more than me. Don't give up hope--bettas are strong fish. Try not to wait too long to start treating him tho.