When I kept ich in my tanks years ago , I used larger uvs and other claimed panaceas to attempt to cope with it; they didn't work overtime. Ultimately, I was convinced the abatement of symptoms in surviving fish was mostly related to temporary partial immunity to the strain by the fish that survived the initial infestation.
It took about 2 years of no new fish for the ich to finally make it's last appearance( one study suggests 11 months duration for a singe l strain without an opportunity for sexual reproduction; I was hoping for that). It would have been easier and kinder to leave the tank fallow for 10 to 12weeks and treat the fish .
Even after months of no symptoms I was still very reluctant to remove them or add a new fish .
Eventually, I decided to err on the side of the micro fauna and bacteria and took them off line with no negative consequences.
I keep over 50 fish and many fry and do add new specimens from time to time.I also take in rescue fish from local aquarists and occasionally from an lfs. I feed a variety of foods as I always have. There have been no signs of ich in well over 5 years
With qt and preventative treatment for new specimens folks can have, with a very high degree of probability , an ich free tank. Just don't let it in the door, and if it sneaks in somehow ,there are proven effective ways to kill it.
This thread may be of interest:
http://www.reefcentral.com/forums/showthread.php?t=2185929&highlight=fish+acclimation+and+quarantine