Green...something forming on water

[Rocketman]

Hey. I left my tank alone for, say, 5 days and when I came back some of the Hornwart had become unrooted and was floating at the top. The center of this 'ball' was coated in green... I'm not sure. Anyway, the water level has dropped in the tank recently, and this has lowered the surface currents, (because other plants have reached the top.) There is also a thin film of what almost looks like soap, but I think this has something to do with having not changed the water lately.

 

[djlen]

Sounds like surface scum. This can happen under the circumstances you outline in your post. I have one tank that develops this regularly. Someone told me to try a female black mollie in the tank and she has kept the surface really clean for me.
It just happens that the affected tank is also my only "open top" tank. Don't know if that plays a roll or not. All my tanks are pretty still on the surface to avoid CO2 loss but that's the only one with this condition. Try a mollie.
Len

 

[wetmanNY]

Or drag a piece of paper towel across the surface. You'll also quickly see whether part of your scum is cyanobacteria.