Is this algea good or bad?

[MiniReefer]

This green leafy stuff is starting to show up everywhere in my aquarium. I have a 20L and it's over 4 months old. Is there anything I could get to eat this stuff? I was looking into getting a blenny.

 

[Brew12]

Looks like Ulva (sea lettuce) which most people would consider good. Lots of critters will eat it.

 

[Bdrake]

Tang crack

 

[MiniReefer]

That's what I thought. The only problem I have is I only have 20 gallons to work with.