Plate has a giant bubble on it???

[maxxin69]

So I woke up today and saw that overnight my plate coral developed a bubble on its underside. Does anyone know what this is or what it means? It doesn't seem to affect the plate, it's still happy and full, just has a bubble on it.

 

[joekool]

That is strange. I've never seen it. Guess that doesn't help. My fungia have never done that

 

[JFrar]

never seen that before, only thing i thought i saw that could be something was the sizable substrate