they don't have to be fed directly, they will grab food from the water column.
If you want them to grow faster you may feed them some mysis. feed each head as they don't always share the food
i dont feed them directly but i do notice my 4 head duncan frag is now a 11 head mini colony within a month time frame. I feed pellets, flakes, cyclopeeze and mysis shrimp alternating each day per week and the duncans grab whatever goes by them through he current.