Ich was last seen on the pec fins of my chevron butterfly on Dec 22. This morning, I notice ich has returned to the butterfly's pec fins. The ich is large already, so I suspect it's been there at least a day or two

The other three fish in this tank (120g), a blue sided fairy wrasse, a flame back dwarf angel and a green chromis have not ever shown signs of ich.
For the past 3-4 weeks, food has been PE mysis soaked with LOTS of Garlic Xtreme and Zoe. To ward off reinfection of ich, the fish have generally been fed at 8 am, 11 am, 2 pm, 4 pm and 7 pm, and sometimes more often.
Also, during the time of the over-generous feeding schedule, the butterfly has noticeably gained weight, and looks and acts to be in very good health. So, dang it, why is it getting ich while the other fish are not?
Am going to feed every two hours from now on to see if that has any effect on the ich.