What lights did you end up going with? The last time I heard you still had Marineland Reef LED lights. Those lights will not support a clam.
Clams need intense lights - usually 8x T5HO systems in 24" deep tanks. Individual reflectors help tremendously. Metal Halide lights are preferred for clams. Clams need a lot of light for their zooxanthellae to produce glucose, but you will need to supplement feeding with Phytoplankton.
Please post your water parameters, including nitrate, phosphate, calcium and alkalinity. We'll know more about your water quality and help you make adjustments as needed.
Once again, those Marineland Reef LED lights will NOT support clams.