16" tall water column with 9" between water and light gives you 25" to the sand bed. I ran my lights 15" above my 24" tall tank with great success (39" above sand bed). If you raise the light up a bit, you can continue with your current brightness and get better coverage. I would likely start by raising it about 5".
If you decide to turn the lights down a bit, I would say cut all colors equally. Your LED lit tank will look about 30% duller than your T5 tank. Every time I look at my tank now (with T5) it's like a glowing kick in the face compared to what it was with LED.
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