I actually think the light isn't too much if you plan on planting heavily. Just load up with enough floaters to cover the surface- amazon frogbit, red root floaters, and water lettuce would do very well. If you can give a few inches gap between the water and the lights, even water hyacinth would be great.
(I agree the light is the upper end.. I use depth as a much better guide for light, but I'm still working on a formula...
if it helps, I use 20 watts for a depth of 12 inches.
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