They are photosynthetic and will grow with just light but they will have smaller heads and slower growth. You don't have to feed every head just a few they share the same stomach if they are stretching then you have fed to much. As far as growth they don't allways stay in a circle they will grow towards there preferred area.
Personally, i'd say i have gotten great growth. I got the frag at the swap in feb. I started feeding a month ago, and so far it has doubled its size since feb. Also, the colors have gotten much brighter.
i suck mysis up through a 1ml syringe (while im rinsing the cube for the rest of the tank) and squirt it at them when the blues are on (or if im behind even when its just the moonlights). i do rinse with tank water though not rodi so im sucking tank water up with them not fresh.