Casey - Did you QT him before you put him in the tank? Was there any major change in the tank that could have brought this on - change in temp, salinity, etc? Now that one fish has it, it's in your tank. IMO, you only have two options: remove all the fish to QT for 6 weeks, or leave them in there and treat with garlic & selcon to help them fight it off. Obviously the first option is the most difficult but the safest. With this option, you'll kill off the ich, but you might kill the fish at the same time trying to get them out of the tank. The second option is less effective - you won't kill the ich so you'll risk getting it back in the future - but you may save the fish in the short-term. Personally, I wouldn't risk trying to catch them all. I would leave them in the tank, feed them a lot of healthy/garlic/selcon food, and hope for the best.