This is extracted from Peteducation.com ...
"The Maxima Clam relies heavily on the photosynthesis of the algae growing in its mantle. However, it should be fed daily with a yeast-based suspension unless the tank is populated with fish and corals which are fed regularly. It also requires nitrogen for proper growth, and if the nitrate level is too low, additional nitrate should be added, but the level should not be higher than 2 mg/L."
I also read the same at clamsdirect.com.