spot on (no pun intended)
i have dealt with white spot many ways, fresh water dip, copper, and doing nothing, i know it might be hard but doing nothing worked best for me, both other options resulted in losing the fish, as the stress caused by moving them when there already sick is normally the beginning of the end from my experience.
just make sure your water quality is excellent, try not to make any sudden changes, and soak your food in garlic juice, this will aid the appetite of all the fish but its the sick one you want to get fat, if he eats well and the water quality is perfect then you have the best chance of pulling him through.