Lawn fertilizers consist of Nitrogen, Phosphate and Potassium compounds that plants use to grow. In this case grass.
You will see on fertilizer labels 3 numbers... 12-12-12 (example--these numbers vary depending on the target use).
That is the strength of left to right Nitrogen, phosphate, and potassium. There are fertilizers that have pesticides mixed into them..
to kill weeds and insects that live below the soil. A common name for this type of fertilizer is "weed and feed".

Nitrogen is used to make green growth by plants. Phosphate is typically used for flowers and blooms. Potassium is used to make strong root systems.

The algae that we are discussing on this thread is predominately stimulated by phosphates.

When you quote a source from the net on NT you need to put in the link where you found it. A short quote + link is spelled out in our guidelines. The explanation and link of this copyright rule is in my siggie for convenience.

The microbiome is the new research in human medicine to help explain how the beneficial organisms in our GI tract and elsewhere...yes, they are everywhere, can be damaged by drugs and antibiotics and then the health of the person is shifted into a disease state.
It is exciting and may provide treatments to help many many people. But this microbiome does NOT include the blue green algae we are discussing on this thread. This algae cannot live and reproduce inside us, and when it dies, it releases toxins that our bodies are not equipped to deal with...these toxins attack cells of the nervous system, lining of the GI tract, skin and other organs like the liver and kidneys.