Neon With White Spot

Sorry guys, one of my neon tetras has a white spot, around 2-3mm large Diameter just below it's dorsal fin. I have no idea what it is, I don't think it's ich though..... but I'm not sure.

I've already quarantined that fish. Any Ideas of how to treat? And maybe prevent it in my display tank?

At the most i'll just kill off that tetra...it's only one. But i'd rather not...