Does your QT tank have a heater? The most dependable treatment for Ich is heat. It stops the larvae get to other fish in its free swimming stage. The temp needs to be slowly raised to 84 -86F. Salt & meds don't really cure much of anything and may hurt more than help. Keep at high temp for one week after last spots disappear then slowly lower temp back to normal. If the fish got Ich while in your main tank, then it's probably already in the tank's gravel and you might have to heat treat the main tank also.
Good luck, OS.