Clam moving itself...sorta

So, I have a blue crocea clam that, in my 65 tall, seemed to really like it's spot.  I bought it from a friend and he said it never attached in his tank.  Well, it attached to the spot I put it in my old tank within a week.  After upgrading my tank, close to a month now, it unattached from its rock.  so I moved it to a spot that I deemed more attractive.  Well, it kept being knocked over.  So finally I kinda wedged it in between two rock where it couldn't get knocked over, I figured it was either turbo snails or urchins.  Well, I was looking in on my tank and I noticed my clam was extending a long white phallic like thing from it's foot.  I thought that it was attaching.  A few hours later it was knocked over.  Drawing from this evidence, the clam was knocking itself over.  I assumed maybe I had it too high in my tank so I moved it down a little.  In the morning the clam was knocked over, off the rock work in to the sand.   So for now, the clam remains in the sand, upright of course.  I'm running 36 3 watt leds with no optics on my 75.  Would anyone else agree that perhaps it was unhappy with too much light and attempting to move itself down?  It's kind of stress right now and I'm noticing a little bit of bleaching in it's mantle.  It's fallen over half a dozen times in the last week.  

Well, after posting I did a bunch of research and found that a lot of people's croceas die when placed directly in the sand.  So I placed him back up high, on a nice spot that kind of conformed to his foot, and he's putting out the long whitish penis thing  out on to the rock.  I guess we will see where he is tomorrow.  There's a couple snails on him right now, danged turbos... grr...they always find the one thing you want left alone for a day or two.  haha

Immediately after my last post he had fallen back in to the sand. I replaced him and this morning, back in the sand. Grr. That's too much to be just snails etc. I'll leave him in the sand.