What’s this on my rock?

[Theulli]

Interesting thing enthusiastically growing on this rock…some sort of encrusting sponge?

 

[blaxsun]

Your tank called. It would like you to scrape the glass the next time you have a chance...

(I honestly have no idea what that is)

 

[WheatToast]

…some sort of encrusting sponge?

Agreed! Probably a sponge and looking great!

 

[Theulli]

Your tank called. It would like you to scrape the glass the next time you have a chance...

(I honestly have no idea what that is)

Haha it is my quarantine tank so I don’t spend a lot of time keeping it spotless. It also has quite a volunteer snail outbreak.
Since this guy seems more cool than harmful I am going to move him into the sump on my DT. Thanks all!