Infected Congo Tetra. Help!

[lordofthesea]

i've just noticed one of my big congo tetra's lips. it has a part of it rotted away! its red and looks like it may have been bleeding, and there's white fungus/skin looking threads around it. the ammonia and nitrite are 0 and the nitrate less than 20. there's nothing that could have hurt him in the tank- no sharp rocks or anything and he's the largest fastest fish in the tank - it's 120l. i've no idea what the problem is!

can anyone offer an explanation and/or a treatment - i've put melafix in the water but don't know if this will help. i have no idea what to do - HELP!!!!!!!!!


edit
he's not flicking or rubbing and there's no excess slime. there's no other fish in the tank that could have hurt him - they've all been there for years and he's the biggest there.

 

[WILDER]

Once the fish mouth rotted away it best to put it out of its misery.
It's flexibactor columnaris. False name mouth fungus.

[URL="http/www.articledepot.co.uk/article-29320.htm"]http/www.articledepot.co.uk/article-29320.htm[/URL]

 

[WILDER]

How many gallon is the tank.
How many fish and which type.
Water stats in ammonia, nitrite, nitrate, and ph.

http/www.thetropicaltank.co.uk/hdcolumn.htm