What is this white spiderweb-like thing?

[stan255]

What is this white spiderweb-like thing? It’s in my overflow box.

 

[JPG Corals]

Looks like a sponge. Should be okay

 

[Solo McReefer]

 

[Kmst80]

What is this white spiderweb-like thing? It’s in my overflow box.

I got that all over the sump and in darker spots in the display. Always thought it was a sponge. My live rock is from Cairns, definitely doesn't do any harm.