I have seen this before in M.e.e. It is called Picta and is not fully understood. I do understand one thing about it. For what ever reason, stop it from doing it any more. Feed it a lot of Romane lettice to help flush out its system. They can pass the rocks and be none the worst or get an intestinal blockage and it is a super serious situation. Keep it seperate it a container where you can monitor the "output. e.mail me direct if you need more advice. Vic morgan