Weird Thing

I have a weird thing growing in my aquarium. Somebody told me it might be bubble algae, so I googled it. It doesn't look like bubble algae. I've only had my tank for about a year, and I havent added anything new to it in several months. It came out of nowhere..Ii can't get a good photo of it, but it basically looks like a thick, dark green blanket with bubbles under it. The bubbles are slightly visable through the "blanket" and some of them are floating above it on a string of... green stuff....