yup, I agree. Fungus.
Salt helps for now but try to get some meds immediately. Maracyn, Jungle Clear, Jungle Fungus Eliminator. I'm sure there are others but those are the ones that come to mind. Just look at the back of the boxes, usually they'll list the diseases it treats. Some boxes will even describe the symptoms.
Good luck
Oh, forgot to mention, the salt says 1 heaping Tablespoon per 5 gallons. 1 Tablespoon is equal to 3 teaspoons so for one gallon I'd put just a little over 1/2 teaspoon.