Brad,
I'm sure Daniel Knop would be a wise person to follow as far as clam advise goes. I don't know much about what clams consume for sure other then what I read and well I geuss just cause I read it doesn't make it true.
What I do know is I don't feed Zoo or Phytoplankton in my system. I geuss I was more disagreeing with your statement that clams need additional feeding. Also I do notice when I feed more fish food that the clams also do better. Wether thats do to the increase in dissolved solid,extra ammonia or the additional growth of phytoplankton(eg. more algae on glass) would be a tough one to answer.