I just noticed about 2 days ago that one of my Cory cats has a pinkish puffy sore coming from the base if its left fin. I noticed that it isn't moving this fin as much as its right fin when swimming. It is still very active and acting normally except its left fin seems a bit limp. Is this a disease/bacterial infection? Or do you think it just injured itself somehow? What should I do to help the little guy? Here's a photo of it.
http/img228.imageshack.us/my.php?image=dsc01392kl5.jpg
http/img228.imageshack.us/my.php?image=dsc01392kl5.jpg