sps are able to thrive with just light, proper water quality, and fish waste like 05x said.
phytoplankton is too small for sps to take up, but they are a basis of food for things that sps may eat. when I used it all I got was cyano
some people do use oyster eggs because supposedly they are good for sps and are the right size. I believe zooplankton are also good for sps and lps.
I use amino acids and trace elements for my sps. Sometimes I dose my tank at night with frozen cyclopeeze.
My home made fish food also has lots of goodies in it. My next round of fish food will have freeze dried reef chili.
another good frozen coral food is Rod's food. He makes a fish food, coral food and original recipe which is good for everything.