What has happened to this zoa?

[Just John]

It's not a disaster, since these zoas grow like crazy, but overnight 75% of the main polyp on this frag has turned almost completely white on the top and the stem and surrounding area are also very pale. What do you think could cause this? Hopefully it won't spread.

Hard to get a clear picture, since it has to be at an angle through the glass.

 

[James_O]

My cinnamon palys did this when they had way to much light, so maybe that is the issue. (They we’re also in a high flow area, but my best guess is that lighting is to blame here)

 

[Timfish]

In addition to James_O's post when a polyp closes up like in your 2nd picture it's going to look very different than when it's open. But if it's colors are very pale when it opens back up it could be bleached, and besides light it a nutrient impalance can cause it. It could also be a bacterial infection which I would not try treating in a display tank.

 

[Just John]

I doubt it's light or flow, since it has been happy here for about 2 months and gone from 1 polyp to 5. I am wondering if a snail might have sucked on it and done this.

 

[Onewolf]

What is the coral to the left in the photos?

 

[ZoWhat]

Bleached out zooxanthellae due to factors like light, infection, nutrients, too much potassium (which you would have had to O.D. a potassium dose)

 

[Just John]

What is the coral to the left in the photos?

That's a hairy rhodactis. One of the two purple ones with a green base in the lower center.