Surface algae

Does anyone have any experience with this? It's like a very fine
grey-green powder floating on the water surface. It appears quite dense,
making very interesting patterns (grey-green swirls) when pushed by the
filter output. If I touch my finger to the surface, it immediately pulls
away leaving a clearing about 4" in diameter, so it's not very thick.

I'm not necessarily looking for a way to get rid of it as most of these
funky algaes come & go without any intervention from me, but I was trying
to collect some info, as I haven't seen this stuff mentioned before. TIA
--
www.NetMax.tk