If i were you, i wouldn't try a clam in the setup you mentioned. The species that can survive under the mentioned light levels get very large. the logical thing would be to buy a baby squamosa or derasea(sp?) however, baby clams don't have enough surface area to get the energy they need from light, and need to be fed often. And they will outgrow the tank. If you had MH or even individually reflected T5's then you could have gotten a crocera(sp?) which would stay nice and small.