Check the PH a few times and make sure that it is stable... Just a side note: you used new water to start the QT tank with right, not tank water from your display... Then you need to get yourself some formalin, follow the directions for the dip in a 5 gal bucket. Make sure you use an airstone in the dip water. After a 30-45 min dip, move the fish to the QT and check for spots. Better to treat inside the 5 gal bucket because you need less medication and you have a clean QT waiting for him when he is done. You can also use tank water for the dip, what you are going to put in there is going to kill anything that could be transfered from your display tank.
If Formalin does not work (sometimes it doesn't depending on the worm), then a FW dip is in order next.