How big is the maxima? What kind of lights do you have over the tank? It sounds like the maxima doesn't like the light to me, but if it's very small, it could be lack of food in the water column.
3 -4 inches I have 4 54 watt t5s and the clam was fine but then it just closed up. Nothing changed with the lights. Also both clams are closed up. Lights are off ill take a pic in the morning