Ok I got me a beautiful little "Dory" fish. The kids had to have the "nemo" I love tangs. It worked out well. So I got my little blue beauty into the tank and was delighted later in the night to see it snuggled in between some rocks to sleep. very cute. After a day or two though I started noticing the slight discolored marks. hard to tell a color to them. Is it common for them to have marks on them from sleeping between the rocks or should I be looking for another culprit?