Grey film on rocks?

[Oscar’s25Gal]

My 25g has been running for 2 months. It is currently FOWLR. Recently I have noticed two types of white/grey film like things growing on my rock, so could anyone please identify them?

Here is a photo :

 

[Thespammailaccount]

Sponge maybe?

 

[Oscar’s25Gal]

Sponge maybe?

That's what my original thought was, thanks!

 

[ReefLab]

+1 sponge. no big deal.