...gotta give more information.
What size is your tank?
What kind of lights are you running and how far from the surface of the water?
What are your water parameters (now and historically)?
What else is in the tank? (this includes both intentionally introduced items such as coral AND unintentional items such as GHA, bubble algae, cyano, etc)
How big is the clam ?
Do you feed it? If so, how (target? water column with the pumps off? etc)? Also what do you feed it?
Is there anything else going on out of the ordinary in the tank? pH/alk/Ca spikes etc? Did you lose power in the outage?