there is no such thing as a small clam, the smallest of the tridacnas is the t. crocea (my avtar) it gets about 8 inches in length but is the most demanding of the clams on light. You need metal halide lighting and need to place it on rock as it is a boring clam and will bore into the rock to gain a foothold. I suggest placement on a small flatish rock and once it is attached move this rock to where you want it.....that way you can move it. If it doesn't like where it is it will throw itself from it's perch which is somewhat stressful for it. These clams under 3" in size need to be supplemented with dts etc by taking them out and placing them in a dish to feed........ good luck! Oh and the others can grow by more than 10" a year to a massive size and deplete ca like sipping coke.....(I also have a 10" derasa)