This white sponge(?) like thing is spreading everywhere over my tank

[Pacifism]

This white sponge(?) like thing is spreading everywhere in my tank.
It started to grow on a piece of live rock in my refugium but now it is spreading crazy into my main tank.

I cannot even tell if it is even a sponge or not...whatever it is it is spreading everywhere

Can anyone help identify what this is and how to kill it off?

Is it beneficial for my tank or harmful?

Thanks everyone!

 

[bob1968]

Pineapple sponge

 

[pinnatus]

They are beneficial. And a good sign that your tank is doing well.

 

[cloak]

The population usually decreases as the tank matures too.

 

[Betta132]

They're perfectly harmless. If you see one or two in a place you don't like, you can remove them... they don't sting.