Ya, I definatly would not have him in the tank with your other fish. He needs to be in a QT/hopital tank. Formalin or Freshwater dip will clear it up, but he should stay in QT for atleast two weeks. *More like a month if you really want to be safe).
So to recap..
Catch him
Put him in a 5 gal bucket with the dip of your choice
Put him in a QT tank
Watch him (and your other fish) for any signs of spots again for 2-4 weeks
Move back to the display tank