I think this depends entirely on what you're growing. I have maybe 5 things that look better under straight blue lighting. The several dozen other specimens just turn dark blue like the rocks and have zero pop even under blue LEDs. They show their best color under 10-14k lighting. You CAN run all blues, but it'll severely limit what will look good in your tank. If all you want are tenuis, lps, and zoas, it'll look awesome. If you want a wide assortment of sps, it's advisable to run some full spectrum lighting.
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