My Derasa clam seems to be shrinking and does not look good. Any ideas? I have had him for three months and he has been doing great. I dose the tank with kent's calcium and also phyto-plancton. The tank is a 90 gallon and is lit with metal halid lights and flourescents. He is located at the bottom in the sand bed. It almost looks like he is wilting away. Any ideas? should I move him closer to the light? Is he starving to death? What else should I feed him?