Plec Has A Coldsore?!?

[peesa]

My common plec has some sort of growth at the side of his mouth that has appears. It looks sort of like a cold sore like a little irratation anyway does anyone know wot this could be?

 

[black angel]

Any chance of a pic? Also tank size, other tank mates, maintenance, filtration and how big he is.
Have you tested for ammonia, nitrites, nitrates recently?