When trying to coax new suncorals I always cover them with something (ie. soda bottle, milk jug, etc) I chop some mysis, mix in a little tank water, then squirt into the container with a turkey baster. Occassionally stir up the water in the container with the turkey baster to stir up the mysis, once they open up and start eating this will give them mult. feedings to each head. I leave the container on overnight without any problems. They will eventually start opening up and will start to come out more and more. I've had mine 2+ years and they are open more than half the day and all night. IMO even if the heads don't open up I think they absorb a little nutrition just letting the food sit on them. When I take the cont. off of the suncorals, the remaining mysis is the food for fish that day. When I first get the suncoral I ususally have to spot feed them every other day, eventually they will only need spot feeding twice a week. Although I feed my tank heavily and they get good flow so they catch food on their own also.
I have read that periods of no or low flow cause suncorals to spawn. Don't know if that is true but I have baby suncorals popping up all over the tank, so I really don't think lack of flow overnight hurts them at all. I do remove the cap to the milk jug though so there is some fresh water exchange.
