All stress factors combine to precipitate a bleaching event, so I would stop focusing solely on the lighting scenario - there is definitely more going on for them to bleach so easily.
Corals growing out and blocking flow to others can be a biggie, even if you didn't make any changes.
Carbon dosing seems stressful if you're doing that.
@Waters, I know this probably is all in the past and you're just bringing it up for example, so this is just hypothetical analysis.
I wouldn't have any faith that the numbers on the fixture could be used like that.
Like you ended up doing, I would
only use either a PAR or lux meter (even a cheapie $15 lux meter is better than eyeballs!) to assess intensity vs any calculator or built-in settings - and it sounds like your levels were very moderate.
Having before and after PAR readings would have been another set of data points though.
There's a lot of bs info and hyperbole floating around IMO.
30,000 lux (600 PAR) is not incredibly low.
Consider these points:
- Stony corals are known to survive down to 1,000 lux.
- 5,000-10,000 lux is where a lot of corals seem to reach their "compensation point" and is incredibly low intensity
- I run a stony coral tank that gets around 14,000 lux.
It grows mostly the same corals as the 50,000 lux display next to it. (Tho probably slower.)
- 30,000 lux is moderate. In fact, right in the sweet spot, I'd say.
Also, lighting intensity is not the end-all....folks using more light than you are not doing anything "better" than you are.
More is not better.
If you move your corals around at the drop of a hat, that's an additional stress factor to consider. Had they been moved recently before this?
Restoring the lights to their previous settings (undoing the change you made) should have been all you needed to do.
Now you have to move them again if you want them back at their original light (and flow, etc) position.....or the coral has to adapt to the new-new flow and lighting conditions. Might be fine in the long run, but in the short term it's another stressor in the mix.
It goes back to the more is not better thing. It's simply a matter of what their corals were acclimated to vs what yours were acclimated to. Neither is better....it's mostly a question of what is normal to the coral.
To that point....if the folks running 100% switched down to match your light settings, their results would be just as bad as you switching up to their settings.
I haven't done any comprehensive studies, but I have had good luck with dying frags without using any elaborate movement routine. They seem to do the acclimation on their own - you just have to remove the stress(es) that caused it. Often (maybe all the time?) that's as simple as bringing the coral home to a nice, well-kept tank.