Possibly coralline?

[DuvalTilWeDie904]

I know this is wishful thinking, but just wanting to know if this is possibly coraline? Whatever this is, it refuses to come off the glass. Thanks,

 

[Tired]

Looks like coraline. Pretty stubborn stuff- you'll need to scrape it off with something hard. If you sprinkle the scraped bits on the rocks, it might spread from there, though it's probably already starting to set up shop elsewhere.