Okay, I am a Herpetologist and usually I know whats going on but this is weird. When i first caught this guy he was a greenish color, due to living in a VERY polluted lake (It was by the Quaker Oats Company) and now I have him in a clean water tank, where he has been fine for the last 6 months. he also lives with a little Snapping turt. Well now he has a white spot on his shell. Its exactly in the middle and is not loose/deterating/bone. He hasnt been sick and is eating well. The other Big SS that I got from the same lake has been doing fine and doesnt have it.