I'm not an expert on Clams, but I think it would quickly out grow the tank as well as need CONSTANT supervision on additives and food. It would filter 6 gallons of water in no time. Also, I'm not sure if even the hardiest clams can be sustained under 40w of PC light. You might get away with the light though. If I had to actually suggest any clams (which I don't suggest you keep one) I would recommend either Tridacna deresa or Tridacna squammosa