I haven't heard of that but, do it's lip look at all cottony etc? What sort of set up do you have and are there any other fish in there? If there are you should move it to a hospital tank if you have one set up and ready for it. You could also try garlic based foods if it's still eating other wise your only options for a fungal infection ,"if that's what it is" is treat with an anti fungal agent. Normally I'd encourage you to attempt to build it's healt more holistically by diet etc . but, if it has an infected mouth it's probably not eating well or at all.
Could you also tell us a bit more about the tank your params tank mates etc.
hth
max