It's normal to just monitor the fish for signs of disease. Treatment is only recommended once the fish shows signs of illness, and the illness has been diagnosed. Otherwise, it would be impossible to know if you were treating for any disease, or possibly treating for the wrong disease. Unnecessary treatment can have a big impact on an otherwise healthy fish. Ick has a 21 day life cycle, so it's always recommended to quarantine (and monitor) for a month, just to safe. Ick is the most common disease with new fish, and one of the easiest to diagnose. Some diseases can be difficult to nail down, but it's better to have a fish die in the QT than to die after infecting all the other fish in the display tank (DT).