So am I correct in saying that although the title is "solving the algae mystery" nothing has been solved here?
Not in a finite sense, although I think clarification has been shared, which should be just as helpful, in portraying that there is no simple fix.
Unfortunately, I often as well do read and even hear the same "black & white" algae myths reiterated that Waterbug has shared, as if algae can be turned on and off as simple as flicking a light switch if only the pond is shaded and plants were put into the pond.
Since there are freshwater algae species that can emit poisons to kill aquatic plants, then simply adding plants to a pond will not "starve" algae. How do ya get rid of this type of algae? Chemicals, elbow grease, or predation involving organisms that feed directly on the algae.
Since there are freshwater algae species that can thrive in high shade, low light conditions much like Hornwort, then simply adding shade to a pond will not "kill" algae. Fortunately, these type of algaes can be significantly impacted by aquatic plants, through creating a nutrient imbalance and the plant itself emitting toxins to combat the algae.
Furthermore, all aquatic plants, including algae, have their own defensive mechanisms as well so this adds to the explanation as to why only particular algae species are experienced in the pond.
Then, in addition to everything above, there are particular aquatic plants that encourage the growth of particular microorganisms that feed on algae.
Why has a pond not experienced an algae that can kill their Water Hyacinth? Well, pond water circulation and filtration as a big impact on this and also to the extent of the pond's location and there is likely a higher predation rate on the algae, whether it is from the koi or goldfish or other critters or other microorganisms.
Unfortunately, I do too often read recommendations that say, "if you do this, then it will ' fix ' your algae problem." Then, the customer comes back saying that it did not fix it and so then they come back again for an answer.
Often times, predation from fish or snails or other stuff is what will be required to try to " fix " the algae problem.
It is exactly what I mentioned in
post#5, and to use Mmathis word "balance", that it takes multiple ingredients so to obtain that balance and this likely will be different for everyone's pond.