05-17-2010, 09:07 PM
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The watts per gallon is not reliable. It works as a rough guide for regular T8 tubes on larger tanks. But on smaller tanks it can be very far off. The important criteria is the type of light and its intensity, and watts is not a measure of intensity, only of power used for the light. You can have a 40w tube and a 32w tube that produce the same intensity; the wattage difference is how the tube is made. Similarly, Life-Glo 40w tubes emit 320 lumens or something, and Aqua-Glo 40w emits half that [may have the numbers off, going from memory].
The other critical point is that the more light the more nutrients will be needed. Tom Barr has written, and I totally agree, start off with the absolute minimum amount of light and balance the nutrients; then if issues arise (as Natalie has mentioned) increasing the light intensity may be one solution.
It is a fact that the majority of aquarium plants will grow fine with much less light that many use. And less light is easier on the fish, and is more likely to avoid algae issues.
P.S. I have 80w of full spectrum over my 115g, that is under 1 watt per gallon, which illustrates the inaccuracy of watts per gallon. On my 70g I have the same two tubes, 80w, and that tank has the algae issues.