10 gallon cfl question

I would start at 6-8" above the water line and adjust accordingly.

I run the same bulb over a 10 gallon but I DIYed the bulb into a standard hood fixture with a foil reflector. Definitely enough light for low light plants. I have moss and Java Fern thriving. It sits directly on top of the tank and I don't have any algae problems. Tank has been running for about 6 weeks...

With the bulb in a work light mounted vertically above the tank it should be about 18-20 inches above the substrate. See http://www.plantedtank.net/forums/lighting/85667-par-data-spiral-power-saver-bulbs-5.html#post904062 At that height one light is probably enough, but 2 would give more uniform lighting.