Bare Skin Patches On A Khuli Loach

[B13]

One of my Khulies has what looks like bare patches of skin on it. This has happened before and they eventually disappeared. It's feeding, swimming and behaving OK (no scratching, etc) and the patches themselves don't look like velvet or white spot because there's no fuzziness, etc and it really does look like flat, bare pink skin!

I've searched the form and browsed Google, but can't find anything, so am I safe to assume that the silly creature has just damaged itself?

My water stats are all OK