Fish pond issue

[basswipe]

I'd like to think of myself as an experienced fish pond guy but I'm having an issue.I have an upper and lower pond system.Lower has fish,upper has no fish but a few frogs.

The upper continually grows this long fine stringy green muck.Standard algae killer does nothing to it and I kinda try avoid using chems anyway.The only way I've found to get rid of it is to manually remove it which of course stirs up botton sediment which makes its way down to the lower pond.And I'm doing it twice a week if its sunny all week.

Is there something out there like an algae killer that will control this stuff?Something natural preferably but at this point I'd consider chems!