It is really hard to diagnose fish without seeing them. This sounds like some sort of bacterial type infection or even sometime "bloat" will at its latest stages will cause the scales to appear to stick out. It would be best to isolate so that if it is contagious it is not going to affect your other fish. You can trying treating with Metronidazole. It is available in several different brands, follow the directions on the bottle for treatment.
It is hard to say what has caused this, it could be stress, diet, water conditions, tankmates, etc.