Feeding a good planktonic food like DT's phytoplankton is going to be imperative for this little guys survival.
I am assuming it is placed in the tank you have listed in your signature. You will have to be very diligent on keeping your water parameters stable. Salinity, ph and calcium are going to be very important. Nano's are tough simply because of stability issues. The lighting that you have is not sufficient for this clam.
Nice looking clam still, do your best. Rob