I just noticed my sea urchin with some white spots. Been perfectly healthy and have had about 5 months or so. We recently lost a Banner fish who was new (2 mo) and was perfectly healthy as well, eating right away and adapted to the tank. Water test have salinity and nitrate all in perfect order ... my local fish guy didnt give any concern if test were good and if no one else died its probably bad luck than a disease, but now I see the Urchin. I guess it could be sand but not sure how it would have got there.