There are a couple of things I have used sucessfully on fin rot. One is AP Anti-Fungus, which works pretty well. Another are the Jungle Fungus Clear tablets, which have worked very well, although they will sometimes stain your gravel or decorations a little.
You should make sure your water is very clean, as this can lead to fin rot. Regular water changes are a must. Angels are pretty suceptible to fin rot. The other thing to make sure is that the tank is at the right temperature, cold water can lead to fin rot, too.
Hope this helps