What is this stuff?

[Treebeard]

For the past few weeks I have had these strands of a clear slimy substance stuck in the power heads and floating around the tank. Tonight I found one large chunk of it in my refuge and was able to pick it up and toss it down the drain. It had the texture of what I would imagine a jelly fish would feel like, however I was able to break it up and push it down the drain. What is this stuff?