Its not something I totally made up

, just something I concluded from other things I've read about acclimating livestock to new lights or new photoperiods. Based on the idea that its recommended to keep lights on a timer, so that the animals have a constant feel of day and night, it would seem reasonable that a sudden switch between day and night could confuse them for a while and could be somewhat of a shock.
I would guess with fish that they would be a little confused, but fine, but anemones are much more sensitive to light changes. Mine changes in appearance between darkness, to just actinics, to actinics and daylights.... he reacts to all those changes. I could definitely see a 24 hour photoperiod causing an anemone to panic a little. They build up there UV protection overtime to account for the amount of light they recieve. An extended photoperiod could cause some shock in that sense.
Also, isn't it the safer way to handle all changes in reef aquariums the slow patient way? I seem to remember the phrase "IN A REEF AQUARIUM, ONLY BAD THINGS HAPPEN QUICKLY"

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I'll just conclude with the fact that with the slow change method its extremely unlikely there will be any adverse affects to the change in photoperiod, with the quick way you could just listen to someone who says "yeah why not", lol.
But yeah I definitely agree its worse to leave the lights off for 24 hours than it is to leave them on for 24 hours.