Fin rot will not affect the scales at all but will be limited to the fins. The fins begin to become transparent or look like they are just melting away or getting frayed on the ends. Sometimes they will develop holes in the center of a fin in very severe cases. Usually the nearer the body the holes or weakened areas get the more severe the disease is.
As far as diseases that affect the scales, that would be another problem and if possible I would need a picture to see what is happening exactly if possible. There are a couple different possibilities.
Rose
