02-26-2012, 09:16 PM
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watts per gallon is almost entirely, and completely useless. I have a 20 gallon long, which is around 12" deep. A 20 gallon X high is double that. The same light on the 20L will be significantly dimmer at the bottom of the 20 X high tank, even though its the same wattage and the same volume of water. Same watts per gallon, totally different level of lighting.
In almost any fluorescent fixture, the bulb thats in there is the only one that will work (as it should). A t8 tube, in a 4 foot length, is going to be 30-34 watts. Period. Thats how much light is over my successful 55g planted.
You can replace the fixture with a custom, or a double T8, but you will need to increase your fertilizers to balance with that much light.