rabbitfish

So I have a 75 gallon tank that’s just under a year old; it has a one spot foxface in it, along with a snowflake eel and yellow headed/fimbriated eel. The eels actually don’t care about each other at all, they really only go near each other on feeding days, because one of them can smell the food...

I added a rabbitfish to my 150 gallon FOWL tank a couple of days ago. I didn't notice it the first day, but the second day I saw it had a pink lump on its mouth. Can someone help me identify it as well as know how to best treat it? my water parameters are 0.0 ammonia, 0.0 nitrite and 0.0 nitrate...