Maxima Clam Question

[pinkreef]

I have had my clam for a little over a month. I put it on the sand first and it wasnt opening up fully but was responsive. The mantle just went over the edge of the shell by 1/2 inch at most. I asked at Safari why mine wasnt opening and he said put it up higher. i have tried that for a couple of weeks and no change so i put him back on the sand because i worried my tang would knock him down. i have 14000k mh lights that are now about 30 inches from him. why doesnt mine open up? barb