I have Neon Tetras that have white nodules growing inside their mouths. What is this? It sounds like 'Cotton Mouth' except the nodules do not look like cotton wool, they look quite solid and a re very white.

Shortly after I got the Tetras (about 4 months ago) one of them had a nodule, but it went away just as I was getting concerned. Now 3 of them have it and one looks like he's going to starve to death because he can't close his mouth at all and is starting to lose his colour. None of them have spots anywhere else on their bodies, so I don't think it's 'Neon Tetra Disease'.

Any suggestions or advice?