I see what looks like an oily film in one photo...are your fish spawning currently? I get what you have from time to time. I think it's a combination of organic decomp on the pond bottom, pollen, and simple scum blown into the pond. I'll bet it clears when you get a rain.
"Forget pounds and ounces, I'm figuring displacement!"
If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.