Rotifers are pretty much the smallest food hobbyists can grow, and you'll need a starter culture which is available online from Florida Aqua Farms. Rotifers are tiny specks of dust basically. In the image above, there are hundreds if not a few thousand rotifers that gathered along the edge of a petri-dish. Video would have been a better choice as they are just too small for my camera to photograph accurately. Rotifers need phytoplankton to live, and this must be provided daily. The rotifers consume the phyto and then they can be feed to fry (baby fish) or to corals late at night, when their polyps are extended for feeding. Reef-safe.
More pictures in this blog entry.