Phyto-feast - Need it?

Bought a very small maxima clam and the LFS guy ( a very good LFS) said the baby clams can't live completely off light yet so feed them something like phyto-feast. Now I got gold/brown cyano on the sand? Connected? Can the baby clam live without phyto-feast? I baste the heck out of my tank and it stirs up a lot of detritus/crud. Can't the clam, a filter feeder, live off the crud?