I used to think they dont need to feed but I am convinced now they do. I saw a huge green bubble at a LFS it was growing fast and actually based itself over the rock it was put onto, very happy coral. The owner said he feeds it all the time and so I started feeding my green bubble coral and amazing it is looking so much better, I feed it thawed krill, it loves them. Do it right when the lights are going out, and the feeding tenticles of the coral come out, you have to watch the fish they can pull the krill out if they are aggressive enough.
Chris