What the most critical factors are to keeping acropora successfully.
They grow like weeds for some, while others can't grow them at all. Low but existent nutrient levels? Plenty of people are growing them colorfully in high nutrients. Stable alk? Plenty of people grow them with regular alk swings. Light? Some grow them at 300 par, others 700. Tank maturity? Sure, but we haven't defined that very well and even then, some grow them in new tanks.
I'm pretty convinced there is something critical we aren't accounting for.