Cup coral discoloration

[Steve Jones]

Came home to see the right side of my cup coral was discolored. A green tinge rather than the fleshy color. And several polyps in that area severely retracted. Should this be a concern?

 

[Tahoe61]

Corals often change color slowly under different lighting types or the lighting type makes the coral appear a different color. Nothing in the current image provide would alarm me.

With LPS and SPS always trouble shoot water chemistry. Stony coral are especially sensitive to swings/sudden changes in alkalinity values and lower then optimal levels.

I would start with water chemistry and continue to watch the coral for any further decline. Make sure no neighboring corals are stinging the coral as well.