Mike, yes, it looks like the one needs to attach to something, otherwise it is very difficult to open and close. Wit was on to something with the lights. Jack had it under less light. If you have them near the top, you might consider moving them down for a while into the sand bed to aclimate to the light. When I kept mine low, I usually put something under them (rock, clam shell) so that the foot could attach and keep pests away, or move them to a more central part of the rockwork. If they are in the middle of the tank, you should be fine. The only trouble I had with corals and aclimation to the light were green ricordias. All other invertebrates did fine. One last thing, don't 'keep' moving the clams. They are sensitive and given too much movement can become stressed and might die.