Deep water changing color?

[JammyBirch]

this is my first sps coral been a great grower, lately I've had some issues with it and elevated nitrates in the tank. This week it's changing from green to purple in spots.

I run an LED light, and my nitrates which are usually ~2ppm have been around 10ppm. I'm slowly getting them down at this point.
Could the nitrates cause this? If not what else could? Is it a bad thing?

 

[ReefWreak]

Nitrates will absolutely change the color of a coral. High nitrates will ultimately cause it to brown out or die entirely. Low nitrates lead to lighter colors and eventually fading of colors. Some SPS experts dose supplemental nitrate to increase colors.

As long as you're getting nice coloration, then it's fine. If nitrates continue to rise, and the coral turns brown, then you should cut back on feeding, increase water changed, or increase skimming to get the nitrates down.

Corals also brown or bleach from other stresses as well, like level spikes (alkalinity, salinity, nitrate), and they can take months to regain their coloration