I have 330 watts of PC on my 55 gal reef tank and I have 3 clams. They are 2 maximas at 2"-3" and 1 3" squamosa. I have had them for a little over a month and the maximas are growing fast. One has grown about 3/4 of a inch. Which is about 4" down in the tank. The others are on the bottom and aren't growing as fast maybe about 1/4 of a inch. All see happy. This is my opinion.