Sun corals are always hungry. Feed it every night if you can for the best growth and highest chance of it producing planula (if you want it to). Feed it a big meal once or twice a week at the very minimum. They will come out at night on their own, but will come out during the day if they're trained to do so. If you see tentacles peeking out while the lights are on, reward it with some food and it will start to come out during the day more. Also if you feed some type of smelly food (mysis juice or coral frenzy for example) at the same time everyday, it will start to open up in anticipation of that feeding on a daily basis. Then from there it should open up more during the day. Hope that helped.
