Whats wrong with my guppys fin?

I have a guppy, molly and one tetra in a hospital tank. They were being treated for ick but they are still in there after the last treatment and no more signs of ick appeared just to make sure before putting them back into the main tank. They've been in there for about a week. The guppys fin and nip marks but instead of it looking torn it has red edges around where it's been nipped like it's bleeding or something..? Shes got long flowy fins and it's right in the middle its not like its close to the body.. What is this?