White and a brownish fam on the surface of the pond is caused by excess protien in the water. Caused I would think by over feeding and or dead and rotting fish/plant matter.
The only way I know to rid your self of the problem is with a "fractionator" a bit like a protien skimmer in a marine tank.
Im bound to have misspelled that ar indeed even given a completly wrong name, so if anyone knows the proper one fell free to correct me.
Mike Driscoll
Dont knock on Deaths door!
Ring the bell and run away!
Death hates that!