Joe, I think maybe you misunderstood. The first new fish brought the ick, gave it to the existing fish, and then another fish was added to the tank while the ick was an issue.
With this in mind, what kind of fish are in the tank? What kind of corals/inverts? That name isn't something I'm familiar with for meds, but if you can give me a list of ingredients and list of fish in the tank, then I can at least tell you if it's safe to try, or suggest another med that would help you safely.
Also, what is the temp in the tank? Water params? You won't want to medicate of there is any ammonia or nitrite at all, or nitrates over 40. The water params would have to be dealt with first so the medication doesn't have an adverse effect on the animals.