Something eating/dissolving my Acro at night!

[Alexraptor]

Strangest thing, something has been degrading the base of my Efflo at night. This morning I woke up to this:

Best image i could get i'm afraid, but i've had this happen twice now, and I've pruned away the affected part. But it starts around a contact point on the rock, and there is usually a white flaky residue left behind at the point where the coral touches the rock. And I should emphasis that this ONLY happens at night.

In addition it is clearly an external source and not STN/RTN, as I've placed the parts that broke off during cutting into other tanks, and they show no signs of continued degradation in their new tanks. It's like something is dissolving/stripping away part of the skeletog, leaving the entire area extremely brittle. And it always begins at the exact point of contact with the rock and spreads from there, and in this general area.

I have a contact point higher up and another one where the colony intersects directly with coraline algae, which are completely unaffected.

Anyone have any ideas?

Edit: Here's a picture from a month ago, when it all started. I've highlighted the small bare patch, and the "white chalky residue" left behind.

 

[Jason_MrFrags]

Any lps in the tank? Some of them get long sweepers at night

 

[ArachnoJoozt]

Maybe an invert like a crab? They are mostly night active.
Have you been observing the surroundings of the coral at night?

 

[Alexraptor]

Any lps in the tank? Some of them get long sweepers at night

I mean, there's an euphyllia in the second phot lol, and I also have a favia elsewhere. But none of them produce sweepers anywhere near the length to hit it, plus the currents don't favor their sweepers either.

Maybe an invert like a crab? They are mostly night active.
Have you been observing the surroundings of the coral at night?

I have, the only thing I've seen poking around is amphipods. Only non-snail inverts I have are a couple of hermits and an emerald crab.

 

[Troylee]

I mean, there's an euphyllia in the second phot lol, and I also have a favia elsewhere. But none of them produce sweepers anywhere near the length to hit it, plus the currents don't favor their sweepers either.


I have, the only thing I've seen poking around is amphipods. Only non-snail inverts I have are a couple of hermits and an emerald crab.

It could be your emerald.. mine was a acro muncher..

 

[Alexraptor]

It could be your emerald.. mine was a acro muncher..

The thought crossed my mind, but he's more interested in crawling on top of it and munching on the mucus, but it's only occured at areas of direct contact with bare rock, and always starts around as a semicircle radiating out from the contact point. There are no marks anywhere else on the colony.

 

[Reefkeepers Archive]

Try to catch him in the act, use a red light and check on your tank every 30 ish minutes at night, once you see him you've identified your culprit, thats how I caught my leptastrea-munching sea spider (to be fair i didnt realize my leptastrea was getting eaten until i caught him lol)

 

[arc.flash788]

It could be your emerald.. mine was a acro muncher..

I got two emeralds a couple weeks ago and one of them only lasted a day. I caught it messing with my zoas one night after I had noticed they were staying closed most of the time. I took him out and put him in the 10 gallon jail tank. It’s so strange because it’s almost like he knew he was doing something bad. Once I looked at him he hopped off the zoas and tried to hide in a rock I had to move my hermit crab a couple days later because I saw him messing with my corals as well! I don’t think I’m going to give crabs another chance. I still have an emerald in my tank somewhere that I barely see so maybe I’ll see what he’s up to when the lights are off.

 

[SamMule]

I would bet its the emerald crab. They seem to be hit or miss. As others suggested, take a look during the night.