I recently lost a battle with my sun coral. It was absolutely beautiful, but you have to feed every single polyp, they do not share food with each other. I would recommend removing the coral from your tank and into a quarantine tank when your feeding it. If you can't do that make sure you turn off all of the power heads and let your tank sit for 5 minutes or so. Get some meaty juice and squirt it on the polyps and then wait for them to open. Once open you can inject some mysis or similar into their arms.
Be very careful not to overfeed this coral because it will pollute your tank in a matter of weeks. Good luck!
Melevsreef.com - Suncoral