Because about 1.5 months ago I switched to an ATI T5 fixture (only tank change) and since then my coral growth has exploded and they are showing colors they have never shown before. I think a pair of XR30s would have done much better than the XR15s (I'm not here selling T5), I just didn't have a spare $1500 to experiment. I think LEDs can work for Acros and Milles, you just need to use about double what is recommended for adequate PAR and coverage.