Saw this on glass just now

[Elielizondo24]

I looked at my aquarium today for the first time in a few days and I saw this. What is it? Good or bad?

 

[cosmo]

I'd say a pineapple sponge, there could be a bloom of them soon, harmless but can get ugly. Usually die off within a month or so, or ya can remove them.

 

[Elielizondo24]

Cool thanks.