I recommend to feed your fish 1-2 pellets in the morning and at night. Also, don't be scared to not feed your fish for one whole day, because not feeding it will help his digestive system cool down.
Chrissi K: I know. I was joking. Of course they want you to buy more, they need the money.
Not much you can do from here, and I'm sure there are other things you can use to cure your fish's fin rot. Check your local pet store. Just keep watching your fish and hope for some better results.Your fish could also have an internal infection that you have not noticed and may not notice which...