Whats the problem with this favite

[Georgio]

I have owned this for 8 weeks It has recently started receding around the edges progressing inwards and inbetween the walls it has what looks like bulging tissue? I recently also notice these long black stringy things coming from a few mouths,
It has been feeding well despite the issue. I also have the same problem with a war coral which I introduced 3week ago
My perimeter are spot on although my phosphate are a little high 0.05
Please help

 

[Shep]

Hard to tell for sure, maybe some kind of pest came in on the war coral

 

[miyags]

When I see this, it's usually low Alk 7 or lower. Try for 10. I also had a problem with anthropodes eating the edges. Look in, with flashlight after lights been out for around 4 hours, See if anything is eating it.

 

[LetItReef]

Had similar issue due to high Phosphate and I made the following:
Did some weekly water changes.
I don't have reactors but I went with Chemi pure elite.

 

[Georgio]

Lfs told me the cause could be that I'm using carbon in my canister filter and to try removing it I always thought carbon was a good thing?