Missing parameter to be able to run High PAR Levels.

[Paulip]

Obviously, too much PAR can be a negative. Yet, I come across these web posts of growing corals at very high PAR 500+ at the top. Strangely, in a mixed tank.

What allows for this? I think it is more than simply the requirements of the coral species. Something that is the province of ULNS systems or moderated Alkalinity (7)?

Thanks for your replies.