GSP Help : Is it being eaten or diseased?

[AndyinAtlanta]

So this started a couple days ago. My tank is 30 gallons, and other corals are all doing fine. I have two GSP spots in my tank and they are from the same initial frag. I had a small water problem a few days ago, likely due to overfeeding, but this has been rectified. Testing this morning everything looks well inline with the normal parameters. The other corals in my tank have been thriving.

On one of my GSP corals I noticed a white area forming two days ago. It got bigger yesterday and even bigger today. Here is a photo (sorry about the quality) from this morning:

The polyps in the middle are completely gone but the rest of the coral seems completely fine. Does anyone know what this is and how to treat it?

Maybe completely irrelevant, but I do have one specific red scarlet hermit crab that loves hanging out on the two GSP corals. The one I found him on this morning didn't appear to have any damage, but I don't know if he's one to eat corals. I moved him to the other side of the tank but he usually finds his way back to the GSP corals (they are both right next to each other) by the morning. Could he be eating the corals? Thank you.

 

[Mr Fishface]

The picture isn't showing up at all, for me at least.

 

[czynot]

It is very hard to kill GSP. Your
Water parameter must be off or not enough lights. I put my money on lights.
What light do you have?

 

[AndyinAtlanta]

I've attached the file if its not showing up above (it shows up for me)

I have a Fluval Marine 3.0 LED light.

Also an update. I was able to scrap off the white substance pretty easily. I sucked it all up bit by bit. It looks like it might have just been on the surface of the coral.