What Type Of Algae Is Growing Under My Aquarium Lid?

[jacx14]

Hi All,
 
So I have had lots of algae growing under the plastic lid of my aquarium, which I keep wiping off. I can imagine that the proximity to the powerful overhead lighting, the heat, plus splashes from the air stone is creating a great environment for it. Its green and forms a thin layer over the plastic which is slimy looking. It can be easily scraped off with your finger and comes off in one whole sheet almost like paper (which you can see if you then float it in water).
 
So my question is... what kind of algae would this be?

 

[Byron]

This could be what is commonly (I think) called Green Dust Algae.  This is actually zoo-spores, and It usually grows on the aquarium glass as a thin sheet, and it loves bright light.  
 
From your description it is also possible that you have cyanobacteria, which as the name suggests is a bacteria.  Some refer to it as Blue Green Algae since the colour is a very dark green.  It is caused by organics in the presence of light.  This tends to form down in the water, sometimes on floating plants, or the substrate, on wood and plant leaves, sometimes on the glass.
 
A photo might help us narrow this down.
 
Byron.