Clams are an amazing addition to a reef. And can be very hardy animals if taken care of properly
I would suggest getting a larger clam 3” or above, the mortality rate is just so much higher in smaller clams.
I would be worried about low par in your case, 150 max is pretty low but I feel clams would be able to survive might have a really slow growth rate. With that I’m not too worried about size it takes maximas a long time to reach 12” especially at lower par levels
I might consider a derasa they should be more tolerant of lower par, however, they do not like a hard rock substrate they prefer to be sitting on sand or lose gravel. And I’m assuming your peak par wasn’t on the bottom of your tank.
given a good few years a derasa will out grow this tank. They can reach +24”