My clam has been happy in my tank under my 260 watts of PC for the last 2 months. I haven't feed it at all but it was doing great anyway. It's always been fully expanded but today i found it to be retracting it's mantle and as today went on he retracted it more and more. What should do. He's at the top of my tank. He's shriviling up and i'm worried about him. What should i do.