Just a quick google search...
In my case, just on my spraybar, it was literally 1 minute it was exposed, and to this day I can't get coralline to regrow where it bleached out 6 months ago. No idea why.
The number one cause of coralline bleaching... sudden increase in light. Some aquarists also experience this without new lamps or fixtures when they do a water change with the lights on... then all of the corallines left high and dry (with the dropped water level) bleach white right down to the water line within 24 hrs
In my case, just on my spraybar, it was literally 1 minute it was exposed, and to this day I can't get coralline to regrow where it bleached out 6 months ago. No idea why.