Is this a bacteria growth?

[bouquet519]

Started noticing the circle in the middle about a month ago. Seems to be spreading. Research seems to say that it’s bacteria growth of some sort. Any ideas?

 

[Diesel]

I don't think that's bacteria, more like a sponge.
Although it has a opening hole and it could be slime from some kind of critter or wrasse if you have wrasses in your tank.

 

[DSC reef]

Looks like sponge growth