Put the fish into QT.
If you want, you can do a salt bath first (take 1 gallon of water out of the main tank, dissolve 1 Tablespoon salt in it, and put the fish in there for 10 minutes). Watch the fish while it's in the salt bath and remove it immediately if it shows signs of distress.
I had this same problem before with a cardinal tetra that got injured on its nose. I'm sorry I don't remember the name of the white cottony fungus....best not to guess at it. But QT is the best way to go so you can medicate that fish if need be.
If you want, you can do a salt bath first (take 1 gallon of water out of the main tank, dissolve 1 Tablespoon salt in it, and put the fish in there for 10 minutes). Watch the fish while it's in the salt bath and remove it immediately if it shows signs of distress.
I had this same problem before with a cardinal tetra that got injured on its nose. I'm sorry I don't remember the name of the white cottony fungus....best not to guess at it. But QT is the best way to go so you can medicate that fish if need be.