Clear but Opaque coating on Platy

[Aquena]

I have one sunburst platy that is clamping fins, the only thing I notice is a sort of smooth opaque coating over fish (as if it swam through egg white color). It's totally smooth, no lumps or spots, just an opaqueness over the body. Any ideas?

 

[flitabout]

It might be ich. It doesn't always cause the spots sometimes they produce a much thicker slime coat although you see the spots 99% of the time.