Yeah, you def want to treat as soon as possible so you can save those other fish. Ich will spread through your tank with the quickness! There is a lot of debate between aquarist/hobbyist about whether it is better to use salt or to use chemicals. As I said before, I prefer the salt/heat method. Some say you cannot dose enough salt with fish like some plecos that do not have true scales, but others have had success with it and no problems. My advice to you would be to research ich treatments and decide what you would rather do.
The salt method is the only one I have ever done, and basically it requires you to turn up the heater in your tank to above 80 degrees and slowly acclimate your tank to about 3 teaspoons of salt per gallon. There are much more thorough descriptions out there, but whatever you do, you need to jump on it. Ich will wipe your fish out and fast!