I get this sometimes. I think it's a floating algae, sort of like green water,
but only at the surface of the water. Like most algaes, the key to controlling
it is nutrient balance. Last time I got it, I think it was because I let
nitrate drop to zero.

If you get your nutrients in balance, it goes away, though it might take
awhile. In the meantime, surface turbulence will help break it up. You can
also skim it out with a jar, the way you'd remove fat from gravy.


Leigh

http://www.fortunecity.com/lavender/halloween/881/