Frogspawn coral bubble?

[bombilate]

Any idea what happened to my frogspawn it's got like a bubble in the middle, water parameters are all ok so not sure what happened or what it is

 

[EeyoreIsMySpiritAnimal]

They do this sometimes. It could mean it's going to split/grow a new head, or it could mean nothing.

Nothing to worry about in any case :)