"rapdor" wrote:

I have read that a tank needs about 5 watts per gallon for successful plants.

It depends on a number of things. The deeper a tank is, the brighter
light you will need to adequately reach the bottom. Some plants
require very little light, some need a great deal.

In general, 3 or 4 watts per gallon is a good range to shoot for
unless you have an unusually deep tank or are growing very light
demanding plants. I've got 56 watts on my 20 gallon tank, just under 3
watts per gallon, and my plants grow like crazy.

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