Beautiful coral, pain in the arse to keep alive. I managed to keep on for about a year. I had it in a very dimly lite cave with lots of flow. They are not photosynthetic, hence the need for flow to bring food to them.
If your able to move it easily the best way to feed them is with actinic only or Lunar. Put it in the sand, cut the bottom off a 20 oz or 2 liter bottle and place it over the coral. Unscrew cap and blast mysis, and cyclopeeze. If its a pain to move it every day or every other give them a small shoot of food with the high flow to get them open. Kinda teasing them with a small taste. Once open cut off all flow and gently blast them(I say gently so they don't close up when you blast) and shoot some mysis and what not at them.
Be care full not to touch the open polyps with turkey baster, they are extremely sticky and youll probably not get the baster back without injuring the sun coral, (tubastrea)
Hope this helps.