Grape Undata STN, Pest, or Damage?

[JaaxReef]

I have this purple Montipora undata that has been growing wonderfully with great color for a few months.

I was on vacation for 5 days and my Alk went from 9.0 to 8.2 in the time I was gone. For some reason my alk consumption went gangbusters and my two part wasn’t keeping up with it...

I noticed a small bald patch on the edge of my purple Undata when the lights were on the next day and I had two thoughts.

1. It is STN from the alk swing (but I don’t know if a .9 KH swing over 5 days would cause that)

2. My pincushion urchin took a bite too close to the coral when cleaning the rock next to it. (He was close to the coral in the morning with a path running by it)

3. Monti eating nudibranchs (but I didn’t see any at night so far and I have a Melanarus Wrasse who would probably make quick work of them once they hatch).

I’m very slowly bringing my alk back up to where it was, but I’m wondering if anyone has any insight as to what might be the cause of those bald patch.

I hope it isn’t a pest. If it was from the alk dropping will it heal on its own? If it is from the urchin, at least I know it will heal up.

Thanks for your time!

 

[erky]

lack of light maybe

 

[JaaxReef]

lack of light maybe

Possibly. The top of it is under about 250 par. The under side is shaded by Itself as it grew.

 

[JaaxReef]

Another option might be this torch coral underneath it stung it. But my flow patters wouldn’t typically encourage it to send a sweeper above it. I’ll check at night once the lights have been off for an hour or two.

 

[jda]

Looks like point-source light death. This happens as stuff grows and it not as big of an issue when stuff is small.

 

[JaaxReef]

Looks like point-source light death. This happens as stuff grows and it not as big of an issue when stuff is small.

So death from shadowing in that spot? It probably won’t recover then...

 

[jda]

You can add T5s to your point source lights like so many other people do. It will help.

 

[JaaxReef]

I just hate the look of T5 fixtures. Maybe I can look into getting a different light in the future.