My whites (Dumper) had a similar but smaller spot (like a pimple) when I first got him. Of course at the time, I didn't think much of it since I had no real experience and Dumper's skin was a wreck. But anyway, it faded away after a couple days but left a permenant white spot that continues to fade where it used to be. His pet store home was terrrible, 6 WTFs in a <5 gallon (dirty) space and I think that may have been part of the cause. Hopefully your whites condition is minor like Dumper's was.