I have such chili coral and two similar, but slightly different chilis.
All of the for a few months after purchase opened only in the evening and night, and closed within minutes, when the light become a little brighter, than dim, even the early light or low PC light from the other tanks within 1 yrd/1m from it. Shading by the thick black screen between them helped.
This palm-shaped light-red kind with slightly pinkish polyps (white, just hint of pink) is sensitive in my tanks to the water quality, not so nitrates or phosphates, but opens more readily in the filtered and skimmed water, than in water, filled with food. Strange, huh?
Had to hung one up because of bristle worms - it become closed for a week or more, I removed 7 bristle worms from it, 2 big and 5 small. Counting, what allergic reaction they induce after contact with my skin, I understand that closure. Another time with being long closed, it appeared that a 2" bristle worm found it's way into the pump and was smashed by impeller blades, this water come to the tank. Removing the worm, partial water change and carbon helped.
They like water flow, but not blasting, just reflected from the glass. Better, if fine particulate matter is filtered/skimmed from the tank - less bacterial and microalgae film on the coral.
The food: eats many times more, than photosynthetic corals. Size of the food should fit in the polyps mouthes. Depends on coral - if the branches are pinkie-finger thick - it may be 500-700 micron (Golden Pearls, Cyclop Eeze or finely blended seafood), if the branches are around 1/4" (6mm) thick - 300-600 micron (by eyeballing, not precise), the same, Cyclops - grinded, smaller Pearls, and ZoPlan.
Feed after they open, of course, and if they open.
Try totally dark place, clean water, no bristle worms - may help. Anyway, they survived for a several months without opening during feeding, then, after moving to another tank - just opened, skinny and far from glorious, but alive.
Good luck!
