A replaced my original tuxedo urchin a couple of weeks ago with a beautiful white tuxedo and since it's arrival my Potter's Angel has slowly been picking away at it's spines. It's 1/3 bald at this point. Has anyone seen this behavior before? I've tried to dig around and find something on this but it's a mystery to me at this point. Water params are all within normal and there's plenty for the urchin to eat for it.