Stress has nothing to do with a fish being attacked by Ich. A healthy, non-stressed out fish, can get Ich just as well as a stressed out fish, but a healthy, non-stressed out fish may be better able to fight the Ich off, though plenty of healthy fish do die from Ich. Ich isn't always present in tanks, as it can be eliminated and kept out, QT fish is a must. Copper is one way of getting rid of Ich, probably the best, but Hypo and the transfer method also do work. Then again it mayn't even be Ich is the first place, as a lot of dieases/parasites cause similar symptoms as Ich.