It does sound like whitespot,
White spot is a parasite, it can only come from water with infected fish in it. It can't survive out of water or without a fish host for more than a few days or weeks at the most. Have you added anything to the tank recently?
It is a freshwater tropical tank isn't it? In which case copper is not required, normally its best to use Protozin OR Esha Exit. Follow the instructions and complete the course, increase aeration during treatment.
Before you start, what fish are in the tank?