You don't want to move it to a completely shadowed area. It's kind of hard to explain. Basically don't toss the thing under a rock. Most hardware stores carry nylon screening that shouldn't rust at all. I have even built a tower out of two pieces of PVC piping and made like a little "umbrella" for the clam only made out of screen.
When it comes to any clams, usually the BEST way is to wave your hand over the clam above the water and see if it closes. This shows numerous things including that it's system is carrying nutrients to the rest of it's body properly. You also want to check for gapeing. The incurrent siphon, the one that looks like a slit on the front and not the little outcurrent one that sticks out on top, should in most cases almost be touching or within an 1/8th of an inch. If it is gapeing, you could ask the someone if the clams are new to the tank. They will sometimes gape if they are acclimating.
If you want to get all technical, ask to see the byssal of the clam. Look under the clam to see if there are bits of rubble or rock attached to the bottom. If there are, then that means that it still has a healthy byssal organ about 99% of the time. DONT go trying to pull that junk off either. Then look around the opening of the shell and where fore-mentioned said foot or byssal would be for LITTLE TINY snails. They will be about the size of a grain of sand, but have long cone shaped shells. These are known as pyramid snails and are bad for the clam (you can research or do a search on this board for pictures of them)
