Perhaps this should be in another forum (lighting, but since we are talking about it bulb reads Aqueon 8,000k Full Spectrum Daylight 15W 120V T8 18"

Somewhere I read that I should have at least 2W per gallon...that would mean I would nearly have to quadruple my wattage, am I correct? How do I do that? I have a single bulb currently. I am thinking that I would buy another ballast to hold an extra bulb? Is the following something that would be good for me?

24 Inch Current USA Nova Extreme 2x24 Watt T5 HO 10,000K Freshwater

If I am only going 2W per gallon, that won't be incredibly bright, right...isn't 2WPG the minimum I should have?