I once ran 2 tubes on a tank, with separate timers. One was a standard white tube, and the other was a blue marine tube. So I had the blue tube come on a couple of hours before the white light and then go off a couple of hours after the white tube. So I had a sunrise and sunset effect. It was actually really cool. I can't do it with my current lighting unit as the 2 tubes are both in the same power cord