What causes Corals to turn brown?

[falconut]

I had a kalk reactor problem a few weeks ago. Water got really cloudy, but levels never changed. Alk = 7.7 - 8.0, Ca = 400 - 410, Ph = 7.8 - 8.0, Am = 0, NO2 = 0, NO3 = 1, Salt = 1.0235, PO4 = 0.

Today (about two weeks from the problem) the levels are still as above. My corals of over a year of looking great (SPS & some LPS) are turning brownish. Torch, Galaxea, Monti-Digi's. Plus, some of my SPS have bleached a little. They started this about a couple of days after the problem.

I though that corals brown because of lighting or high NO3 & PO4. What else could it be? Any ideas?

[atty]

What is your temp? corals can bleach when the temp gets to high.

[addicted_2_reef]

poor lights?...gone too yellow.

[falconut]

atty - My temps are between 80 - 84 (max). They've been doing this all summer, so I doubt that's it. I think the bleaching had to do with the kalk problem.

addicted_2_reef - The lights should be fine. The one is only a couple months old and the other doesn't need to be replaced until Dec.

Any other ideas?

[skireef]

There are too many theories. One I like is that with excess nutrients, the xoxanthelle (spelling?) within the coral tissue reproduce rapidly yielding the greater brown color. A second that I have seen in my system from time to time is when a coral bleaches, it is repopulated with the xoxanthelle (?) available from the other corals in the system/water column......I have the same exact corals as frags with different colors as a result.

[PatrickJ]

zooxanthellae*