i actually have this exact tank; you can see the link in my sig. I kept the Double Bright and added the Single Bright. I measure a par of high 30s to low 40s at the substrate, and grow various Crypt species, a Taxiphyllum sp, and a Ludwigia sp. while the Double Bright only has 9 LEDs, it's markedly brighter than the Single Bright with a much higher PAR. by the time the light hits the substrate, it will be somewhat more diffused and spread out, though I admit that my Ludwigia grows toward the individual nodes once it gets within 6" of the surface or so. I can tell you that you may gave trouble growing anything other than Bolbitis, Microsorum, or some mosses with just the Single Bright, and slowly at that. the best advice I can give you is to add light.
Bump: if I had read more closely, I would have seen that you did add more light! at any rate, i'll subscribe to this thread and see how you come along!
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