What Would Most Likely Cause This?

[55semireef]

I've had this orange/green digi frag for over a year, and I swear this thing has been through hell and back. Dinos, cyano, two blackouts, massive alkalinity swings, and basically every mistake I made while learning to keep SPS. Nothing ever seemed to faze it. Easily one of the hardiest corals I've ever owned.
Recently, I moved it from my 40-gallon frag tank into my 90-gallon display, and within less than 24 hours, a section was suddenly nothing but bare white skeleton.

What's strange is how clean and defined the damage is. It almost looks like I dipped my thumb in bleach and pressed it against the coral. The tissue loss hasn't progressed whatsoever since I noticed it. No peeling, no additional recession, nothing. That's what makes me question RTN or STN, especially given how suddenly it happened. I've inspected for SPS pests and haven't found anything obvious.

Current (stable) parameters:

Alk: 8.0 dKH
Calcium: 450 ppm
Nitrates: 10–12 ppm
Phosphates: Between 0.08 - 0.1 ppm
Salinity: 1.025
PAR: ~150-200

I'm genuinely stumped. I'm starting to wonder if a crab or some other nocturnal pest is responsible. Has anyone seen a crab cause this kind of damage to SPS like this? Does predation typically leave behind sharply defined patches of bare skeleton like this? For a coral that's survived nearly two years of everything I've thrown at it, I find it bizarre that this could happen practically overnight.

 

[Baldyreef]

I've had this orange/green digi frag for over a year, and I swear this thing has been through hell and back. Dinos, cyano, two blackouts, massive alkalinity swings, and basically every mistake I made while learning to keep SPS. Nothing ever seemed to faze it. Easily one of the hardiest corals I've ever owned.
Recently, I moved it from my 40-gallon frag tank into my 90-gallon display, and within less than 24 hours, a section was suddenly nothing but bare white skeleton.

What's strange is how clean and defined the damage is. It almost looks like I dipped my thumb in bleach and pressed it against the coral. The tissue loss hasn't progressed whatsoever since I noticed it. No peeling, no additional recession, nothing. That's what makes me question RTN or STN, especially given how suddenly it happened. I've inspected for SPS pests and haven't found anything obvious.

Current (stable) parameters:

Alk: 8.0 dKH
Calcium: 450 ppm
Nitrates: 10–12 ppm
Phosphates: Between 0.08 - 0.1 ppm
Salinity: 1.025
PAR: ~150-200

I'm genuinely stumped. I'm starting to wonder if a crab or some other nocturnal pest is responsible. Has anyone seen a crab cause this kind of damage to SPS like this? Does predation typically leave behind sharply defined patches of bare skeleton like this? For a coral that's survived nearly two years of everything I've thrown at it, I find it bizarre that this could happen practically overnight.

this is very very bizarre like you said, by how clean it is and the way the tissue has died and or disappeared makes me believe it was eaten but I really don't know other than that. maybe @Mr. Mojo Rising can help?

 

[55semireef]

Maybe this is a bit of an assumption but I feel like if it was some sort of parameter or bacteria thing, you would see the coral overall looking in poor shape. This coral literally looks perfect from the other side, but when you turn it around - bare skeleton. Like I said, it's almost as if I touched it with bleach and it seared the SPS skin. Idk...

 

[Mr. Mojo Rising]

IDK but hope you update in the morning, hope it gets better, good luck

 

[Baldyreef]

Maybe this is a bit of an assumption but I feel like if it was some sort of parameter or bacteria thing, you would see the coral overall looking in poor shape. This coral literally looks perfect from the other side, but when you turn it around - bare skeleton. Like I said, it's almost as if I touched it with bleach and it seared the SPS skin. Idk...

yeah especially with what you said about how its been through hell, its clearly hardy which makes it all the more weirder

 

[55semireef]

IDK but hope you update in the morning, hope it gets better, good luck

Thank you. This happened two days ago and it hasn't gotten any worse but not knowing what caused this will drive me insane until I figure it out lol