Hi John, long time no speak LOL
Ah the old Sun Coral debate
Well tbh john I never had any trouble keeping this alive even after being attacked by mushrooms and rics.
Initally they will take some time to adapt to your aquarium, I have found however in recent weeks mine opens quite regularly now the reason for this is the flow.
I have a new Tunze 6055 pump connected to a single controller which has a feeding button on it, this knocks off the pump for feeding. The pump remains off whilst the fish are feeding and returns automatically to normal status after 8 mins. When the pump comes back online and the flow returns, then the Sun Coral will open.
This is a fairly recent observation but it happens everytime.
So try the flow and non flow method.
I feed it Frozen Mysis, Brineshrimp, Krill pacifica and Cyclopeeze. With a large syringe with airline attached to the nozzle.
I dont find that you need to hide these corals in some dark corner, If you look at the pics, mine is in a quite open position. Hiding it also make's life difficult for feeding.
Hope that helped somewhat.
Yeah I hope I can do the new project justice, so many ideas milling around in my head but as always so little cash. LOL
Regards
BigC