Ya when I got mine, I placed it on the sand. I then found out it needed to be on rock and high up in the tank due to my lighting. (460w CF
on a 75g)
It was trying to attach and had dug down a good way, but it came up pretty easy. I placed it on a medium size flat rock, then placed that rock up top of the tank. The clam attached in like a day or two and has done great ever since. I guess its doing well since it has had no color loss.
Here is a pic of mine when I first got it and now:
You can see the clam at the top/middle of the tank. Sorry for the dirty tank...