keep an eye on the LMB, some have had problems with them in the past. i never did, though he did like to sit on the clams scutes.
the panther grouper is not a reef safe fish and gets very large very fast. he will eat any fish or inverts he can get in his mouth, you may want to reconsider this choice.
to test if it is one of the fish bothering the clam, use half a pop bottle with some holes for flow to cover the clam. if the clam starts to open, then you know he is being harassed.
to check for pyramids, look under the clams mantle or in his scutes a few hours after lights out. they are a small white conical snail.
you say you don't dose much, how do you maintain Ca and Alk??
and please list your current parameters.