Algae id help

My tank seems to acquire a new type of algae. It's dark green and it forms
a very thin sheet of film mostly at the water surface. When I took it out, 
it looks like a patch of thin strands glued together (just like carpet but
much thinner and shorter strand. I think it developed right after I had
floor fan blowing across the water surface to cool down the tank during
hot days.

Does anybody know what it is  and how to treat it ? Is this blue-green algae ? 
I wish there is a good pictorial guide to algae. Maybe we can start one
for the Krib. I'll take picture of these algae as soon as I get my camera
back from the store.

Thanks for your help.