Is this some type of Algae?

[Blue04]

Have a bunch of this growing on one side of the tank on one rock, not sure what it is but it's spreading like a wild fire. Anyone know what it is?

 

[jk1138]

I have neer seen that before, but it is hard to tell from the pic.

 

[Blue04]

That's the best picture i could get, it's just a bunch of white strings, almost like grass lol.

 

[Newbie Aquarist]

I believe those are some form of sponges.