This only concerns acropora for the most part. Things that typically have good PE during the day, birdsnest, montipora, goniopora, etc are great. They all tend to close up at night. I have a matted filefish I moved to the sump awhile back. He had been picking on coral and I caught him destroying a favia. All the acropora are doing well and growing, but day time PE is minimal at best. Even the new green slimer I added that had insane PE in the original owners tank has minimal PE during the day. Better PE at night. A tort I got from the same person has awesome PE at dusk/night, but not much during the day. I know this is similar to natural conditions, but my understanding there is the presence of predators during the day. Other corals that are more open at night than the day include: favia, certain gorgonians, sponges. Do the acros sense the presence of the filefish and coupled with the light believe there is a predator? Just looking for some input.