put him in a 30 or 40 breeder and treat him. looks like external parasite. Use external parasite med with good water current, Water change everyday. Should heal in a weak. That's if that was my fish.
If not that then it's fungus.
I agree it looks like Flexibactor columnaris, if so turn your heaters down to below 82'F , the bacteria is most virulent 82' and above, do lots of water changes, and vacuum with a vengence.
I would drop the temp to 76° range. Any medicine that contains Metronidazole is typically good, or grab Fish Mox. Remove carbon, and lots of water changes like others suggested.
It most certainly does appear to be a case of flexibactor columnaris. Personally I would not treat with metro. See the articles below for more info on this disease & how best to treat it.