The question is, why do feel the need to supplement your diet with Spirulina blue green algae?
Why not eat peas or broccoli?
Spirulina is cyanbacteria, a group of bacteria that have the capability of photosynthesis. They grow best in high nutrient, eutrophic waters, often with very little oxygen because of the decay from such organisms. They especially grow well downstream of inadequate wastewater treatment facilities, namely sewage. I trust for you to learn well where the source of your Spirulina is before you ingest it.