I have a 2" Ultra Crocea Clam. It's been about 4 days and it has looked great every day. Earlier today I noticed on one of the "lip" section that it had a white lining instead of the all dark blue. Now when I got home the clam is closed and all I can see is the white lining instead of the blue part. My params are usual good except for nitrate at about 15. Could something be bothering it like my Flame Angel? ( I haven't noticed this though) Could Nassarious snails also be a problem? Should I try to feed more nutrients into the tank? Dose calcium (I have been using Purple Up every night)?