I have only done this once in the past on my 29 gallon biocube. I'm thinking about doing it now on my 90 gallon tank. I'm starting to have some algae problems so I need to address them. Can anyone please advise if they have done this on a large tank? Also if I do this do I need to turn off the led's I'm using for the moon lights? Also I was thinking of doing a water change tomorrow but if I do the 3 days of darkness should I wait to do the water change until after the 3 days are over? Please help me out with this. Thanks everyone.