I had from 12k to 14k over the years. 400w then reduced to 250w because I thought it too bright.
I had macro in a refugium with nutrients too low to grow Chaeto, so ya, low nutrient is likely key... though this suprises me. At times I've struggled to get corals to color nicely... just never the Purple Cross
It had nice color from the day I put it in the tank till the day I took it out.