Maxima Clam Question

[Aquattro]

Barb, your light is fine, even on the sand. My clam has been under MH, LED and T5, all while on the bottom of the tank. Ca needs to be above 380ish, no need to go higher than your 410.
If the mantle isn't expanding, inspect it at night with a flashlight, looking for small snails around the edge. Almost like small grains of rice.
If you can get a good quality top down pic, that might show something. Maybe pinched mantle, which can be treated by soaking it in fresh water for a while.

As mentioned, make sure you don't move it if it feels attached. That will likely kill it.