I will guarantee you that most tanks have ich in them already. If the fish isn't dying, then leave it. You will only stress it out more trying to catch it increasing its chance of dying. soak your foods in garlic or selcon and most likely you will be alright. Most healthy fish will fight ich off. Ich isn't a death sentence after all. Also, when you go to catch a fish to place it in a QT, you are going to stress the other fish out as well, they stand an increased risk of getting ich as well.
40 Gallon Breeder/2x BioCube 14's
2x Aqua Clear 50 HOB
T5 Lighting 4x 36 watts (2x 10,000K, 2x Actinic)
45 Pounds Live Rock and 20 Pounds Live Sand