Interesting. I've never heard of this before as a possible reason for poor PE.If nutrients and water parameters are good, and after several hours lights out (brightly lit room where your tank is doesn't count), your SPS should have excellent PE. If yes, than your tank's light is too intense for them. I have a lot SPS that lives within tidal shore lines and they don't like blinding light intensity even though they came from a 3 feet of water during low tide.