a stupid question....

turn it off

just like you and I, fish need a period to rest and with the lights on all the time it could be a little stressful. a good photo period (the amount of time the lights are on) is 12 on, 12 off. are there any live plants in the tank? if you don't have live plants the photo period is more forgiving.
 
I do up to 8 hours a day with the vanity light located over my fish tank, since I don't have anything but hardy plants in there.
 
If you don't have any plants I'd only turn it on when you look at it (make sure when you do the room lights turned on first, so the fish doesn't get too surprised). Without something to suck up the nutrients, like plants, you're just promotin' the algae. Fish are fine as long as the room isn't pitch black.
 
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