Is My Crocea Clam Ok?

[thamobster]

hey i bought a croea over a month ago and when i put it in it was doing great..its got plenty of light and the calcium is good..it would stay wide open and responsive but for the past few weeks it hasnt been the same..it closes up not fully but more than it should...then if i move it to a new location it will be good again for a few days then close up again..ive moved it to its third spot now and its contiuing to do well for a few days then close up..its foot is attached to the rock its on now though so im not sure what to think..is this common with this clam

 

[f1shman]

What are all your water paramters exactly and what type of lighting do you have? And no tahts not really common in clams.