White Algae? Not sure what this is

[madhattertcm]

So I've been noticing this white fuzzy stuff growing in two different locations. They both look like cotton. One is thicker than the other, but the lighter one is thickening up.

What is this stuff? I can't seem to find much about it.

 

[FishyReef]

Maybe a fungus or a sponge? I'm not sure....

Cute dwarf angel, by the way!

 

[Bifferwine]

I think it's a sponge.