Black Moor with Reddish Mouth Sore

Question
He shares the tank with a Calico Fantail, a Plectostomus and a smaller Black Moor.  I had another Black Moor who had the same red swelling and it grew larger and he eventually died. I love my fish and I don't want him to die, but I don't know what to do! I'd appreciate any and all help I can get! Thanks!

Here's two pictures I took of him:
http://i30.photobucket.com/albums/c329/xifaur/S5000124.jpg
http://i30.photobucket.com/albums/c329/xifaur/S5000135.jpg


It is a 25 gallon tank and the temperature of the water is 70 degrees. The Nitrate, Nitrite and Ammonia levels are at 0 ppm and there are no traces of chlorine.

Answer
Hi Raul,
  Is there any chance that this fish has been fighting with the other goldfish?  Fighting is the most common cause of mouth and lip injuries.

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>