blackout length without killing coral & nem

3 to 4 days is all I would do as the Nem will have the hardest time. residual light does not give algae enough light to grow but that is if it is in a basement with very limited light. When you start your lights back up use the itinics only for the first week 2 hrs on 2 hours off 2 on 2off then add a 2on and 2off the second and third days. Let it run that way for a week then add in 1 10k on for 2 hours for 3 days then 2 10k's for the rest of the week on for 2hrs only the third week you can increase the itinics to 3 hrs on 1 off I would see how that works and adjust the lightings. I had to do this for 2 months to get ride of my algae problems that came about from a digital timer being wired backward. The fish didn't like it at first but they adjusted and then it didn't seem to bother them. Remember a storm on the open oceans of the world can last for days and weeks if there are several in a row. Also with the lighting I am assuming you are this is for T5 HO lights it should work for MH and T5 or MH and PC.

Bill