The fixture sounds like it is HD's model number HBSL-16, if so it is a solid fixture and ballast, many many people use these over their tanks. It does have an electronic ballast, it is an instant start one from advance ballasts. (you can tell because it says it will run several different wattages, only electronic ballasts do that). I agree with Niko, your problem is most likely the way the fixture is wired, it won't work well with only one tube in place, try the aqua glo along with a standard bulb in the other socket, and ,make sure the aqua glo is seated properly.The light fixture said that it accepts 25, 34 and 40 watt bulbs.
I have a feeling that the problem is the balast being a rapid fire and not an electronic balast.
The bulbs labeled "Daylight deluxe" are the perfect choice for a planted tank.Does anyone know about the bulbs from HD that I can use for an aquarium. I am on a budget...