So IMHO, you need to turn the temp up in the main tank slowly over the next week or 2. Then add Epsom salt once you have it high enough. This will help kill the ich and at the same time aid the fish's gill function. Do weekly water changes, adding the salt back every time. The more time that passes, the less ich you will have in the tank. I've heard that it can take up to 8 weeks to kill all of it. I did it for 5 or 6.