DERASA is the hardiest. It is known. Next hardiest GIGAS, SQUAMOSA ,MAXIMA, least hardy is CROCEA.
Strong illumination. No Angel Fish. I like placing on bottom of tank. If clam is not opening , a fish may be picking at it. This will kill clam pronto. Occasionally , there is a tiny white snail on shell, that can multiply and kill a clam. Check outer shell of new clam, for these. A tiny bit larger than grain of rice.