What is this String substance?

[FishmanJosh]

What is this? its vvery fine stringy substance and i have it all over my tank now. Its probably nothing to worry about, I just wanted to make sure.

 

[Kurt_Nelson]

Looks like some type of algae to me. Looks kinda nasty and aggressive... I wouldn't consider it "nothing to worry about", especially if it's all over your tank.

 

[melosu58]

FantasyReef Databases-Viewing item "10 Step Plan for Nuisance Algae Control"

 

[quaqa88]

I'm not exactly sure what it is, but it looks invasive and I recommend removing it before it gets any worse.

 

[Jaybird]

I'd try to pinch that stuff off at the base where it connects to the rocks. It looks like hair algae gone grey