Your water color in the quart jar to me looks like a very strong bloom of phytoplankton. It takes a microscope and an experienced algae person to identify what planktonic algae species are most abundant. Since the water has a green hue I suspect most of the species are the common green algae species and very abundant. Lots of this type of algae are thriving on the nitrates in the water from duck manure to the point of using all the available nitrates thus your chemical test of nitrates = 0. Nitrates grow lush grass and abundant algae. When the nitrate becomes limiting often cyanobacteria begin to bloom. Lots of cyanobacteria species when abundant can also make the water very green. Be watchful of floating green surface film that suggest cyanobacteria that are known to be harmful and problematic.

PS Blue dye as Aquashade when added to water your green will not turn the water a nice blue hue. It takes blue dye with some red in it to make that very green water appear blue.