Microscopic Picture My guess is that your pond contains a specie of Lyngbya (which is a genus of multicellular filamentous algae that are commonly found in a wide variety of habitats).
If correct, I really can't suggest a chemical control measure. I've had customers trying everything (legal) but the kitchen sink, but to no avail.
Based on the size of your pond, your best option may be to invest in a quality aeration system and/or try a good nutrient-reducing bacteria treatment program.
Good luck.
KD


Kelly Duffie
Cypress, TX