Bleaching ?

[Z06-Hec]

Is bleaching only caused by high light intensity ?

My lights have been adjusted for some time and they do not go higher than 35% intensity but some of my Frogs are starting to look bleached. Whats even more weird is I have a colony of about 7 heads and its the lowest heads that sit under the other heads that look bleached instead of the highest ones getting most of the light...
I then have another set of frogs at same height and they look great.

Is this cause of the light or something else?

 

[Tahoe61]

Different corals different lighting needs.

Corals will pale or change or loose Zooxanthellea from use of too much GFO, lack of nutrients (nitrates and phosphates) not enough light or too much light.

First check your chemistry, including N/P, perhaps feeding more will resolve the issue. Cut back on media products if that is the issue.

Always check for pest like Red Bugs.

Put up an images and some chemistry values to assist us in assisting you. What corals specifically are you having issue with? What is the brand of fixture.

 

[hart24601]

As stated bleaching is caused by lots of things, and it becomes more frequent when a few of those things are combined. Temp is a big one, and this paper had really strong bleaching with temp and low pH:

Ocean acidification causes bleaching and productivity loss in coral reef builders

Flow is also linked to light intensity, when over illuminated corals dissipate the extra energy with heat. Increasing flow helps them deal with very intense lights too. It's interesting to think about people bleaching coral with LEDs that might have low pH and lower flow while keeping the tank in the lower/mid 80's - but how often does that get brought up?

Coral can also lighten up as Tahoe said from lack of nutrients - I had to dose nitrate at one point and it worked really fast to bring colors back. I don't know if that is true bleaching like the examples above when the coral expels zooxanthella or if they just lose pigment. Considering the recovery in my case was very rapid when introducing nutrients I don't think the coral expels them like with light/heat/pH, but they look bleached anyway.