I feed my sun coral a mixture of DT's, cyclo-peeze, mysis, plankton, and krill. I turn my power head off, and use a turkey baster to make sure that each polyp gets fed. I have a lot of sun coral all over my tank, so everything in my tank gets pretty well fed. I have to do about two water changes a week, to keep the params. good though, since the tank gets fed so much.
Here are some pics I just took. Thay are open-ish right now, but when they are fed, they are easily three times bigger than in the pics! (I will post pics of them when they are fat and fed tonight.)
The partially dead orange colony in the last pic is relatively new. The person who I bought them from did a horrible job of fragging, and all but that one polyp died! It is eating and growing now though.
I have to say they are my favorite thing in my tank, that's probably why I have so many!