^^ I find myself leaving the lights on longer and longer in an attempt to get some algea to grow for my otos. I dont mind algea, i think it adds to a tank..I have a fake log that is covered in algea and it turned a rather obvious peice into something that looks natural. But i do have dark periods, cause when i do, i see all the fish go to the bottom, and 'rest'. Some dont, Some rest when the lights on, but when the light is off, and you look, there are snoozing guppies on the sand. And my cories too. they always take much longer to wake up, even after the light has been on for a few minutes..they are deep sleepers!
My betta, he sleeps..everywhere, anytime...He finds the coolest beds..=]