Unfortunately, new tanks do tend to get disease outbreaks. The fish are stressed by getting acclimated to a new tank, and the tank itself may not be established enough to be all the way out of the cycle. That adds more stress.
I would NOT go adding any medications to the tank at this point. Keep it clean, and keep an eye on the affected fish. Often, trying to medicate when you don't know exactly what you are dealing with hurts more than it helps.
Good luck!