mine move as well, but only a couple inches here or there, except one that decided to land on the carpet anemone... all I got was the shell back :(

Thanks everyone :)

So the thing is, they move around the spot they are placed to find a comfy spot right? Nothing more than couple of inches..

A day sure. If they moved a half inch a day in a couple days it settles in. I have a clam that launched off the rocks.

I am planning to get something that stays on sand. Can't risk on rocks :P

I have a crocea and a maxima... neither have moved aside from adjusting their angle.
I've kept the crocea on sand and rock. seemed to like both, however I did notice that on the sand, small bristle worms would take shelter under it and probably annoyed it to a degree.

I picked up a maxima from the big Cook Island order from Blue World last year. Being an ultra grade, I figured it would want extremely intense light, so up high on the rocks it went. Came back the next day to find it laying face down on the sand. Tried a little lower down and the same thing happened. It has been on the sand ever since and it doing just fine.

I have 4 clams, a large maxima ultra, a large croccea and 2 smaller croccea. They are all together right underneat my MH and they love it there, so none as moved.

Your light is probably not good enough for a clam and it's looking for a better spot. It will move until it find a proper spot, if there is one.

How big is the clam? smaller clam need regular feeding or they will die and melt. Their mantle is not developped enough to sustain them. Clam of 4" or more are ok, but it is always good to give them a bit of live phytoplankton once in a while.

Not necessarily. My maxima was only 1.5" and did not need any supplemental feeding. I was a bit uneasy about buying one this small but was assured by Ken @ BW that he'd be just fine without feeding. He gave me some live rotifers but I didn't have to target feed at all. Just threw a capfull in the display every day.

Clams eat phytoplankton. YOu may have had enough phyto in your tank.

It is well known that most of the baby clams don't make it and need feeding. YOu were lucky.

Some stores here don't even accept clams under 3" because they melt a lot.