Tell me about brownouts

[eros]

One of the corals I traded a local reefer was a nice white when I got it but now has turned an ugly brown. It came from a tank with MH lighting and I'm running T5's so I figured my lighting would be less intense and the coral would be fine. I'm not sure what kind of coral it is. The same thing has happened to a Stylopora that I bought. It still have nice green polyps but the skeleton has turned brown. All my other corals are bright and vibrant.
Is this a lighting issue?
Is there any chance that these corals will get their original color back?

[Capt_Cully]

Check your nitrates

[tmz]

When ther is less light the coral will respond by growing more zooxanthelae to process more of the available light. It will also make less light shielding pigmaents. High nitrates also feed zooxanthelae growth. Zooxanthelae is brown.

[eros]

It must be my raised nitrates. They've recently jumped from 0 to 40 ppm and I have no idea why. I've been dosing vodka for 2 weeks, so far no change.