Ich is always in a system, you never get rid of it. When the fish are healthy, they will suppress it from showing. When they are stressed, that's when it shows up. Copper will kill off the visible manifestations of it, but it will not erradicate the problem. The best way to fight ich in your system is to get your fish as comfortable as possible. Keep temperatures stable, keep the SG stable, and feed them healthy foods. Putting them into a quarantine now will stress them out more. I would highly suggest feeding them foods soaked in garlic, selcon and vitamin C. Good luck with the ich, I know it can be a royal pain.