Ah you're describing them exactly - white little squiggly circles! I've googled what you say though and yes, it looks exactly like "keratin stress" and he is indeed growing really really fast.
It makes a lot of sense because he eats EVERYTHING and I'm worried my hubby is overfeeding him. I just give him weeds only, but hubby is supplementing with "tortoise food" and shop bought salad!
I will certainly be doing some more research into this!
Thanks so much for you reply, I think that may be mystery solved already
I'm not sure how to post a pic up, my membership says I can't!