The number one sign of fin rot is a blackish or brown discoloration around the edges of the fins or the fins will look ripped. It is treated by doing at least a half change every day while adding like half a teaspoon of aquarium salt. You can move them into a QT tank if you would like. Makes it easier to treat if you choose to use medications and if you have any tank mates or live plants.
To upload a picture it is a little bit of a process.
You click advanced, then hit the paperclip icon which opens another window. Upload it there and exit out of that window. The picture will now appear in your post.