That ich med you bought doesn't really work -- there are only two proven ways of killing ich: copper treatment and hyposalinity. Anything that says "reef safe ich med" is not effective against ich, and is usually not reef safe either. You should never dose any medications in your main tank because of this.
There are different approaches you can take. I prefer to let fish fight off ich themselves. If they have a good diet and good water quality, they will usually never show symptoms of the parasite or get sick from it. Ich really only ever has a chance to get ahold of fish when their immune system is already compromised or when they are stressed (that's why adding a new fish often causes ich outbreaks).
I have never lost a fish to ich, but I soak my fishs' food in garlic extract and vitamins to keep them healthy.
The other approach is to remove ALL the fish, put them in a quarantine tank and treat them with either copper or hyposalinity. All of the fish must be treated, because ich needs a fish host to survive. If you remove just the sick fish, treat it, then put it back in the tank with the other fish, he'll get ich all over again. The only way to kill it off from your tank is to treat every single last fish. The fish will have to be quarantined for around 2 months. So this approach is a hassle, but it will rid your tank of ich (but you also must quarantine and treat all new fish in the future as well).
I've always taken the first approach. As long as the sick fish is eating, the ich will probably go away on its own.