If cyanobacteria "outbreaks" are associated with raised levels of organics then the trigger rise in ammonia level might be really small. Cyanobacteria are like diatoms and pretty much universal on earth, I would guess all tanks will have some present at low levels.
I may have asked you this before but have you ever taken a sample of slimy BGA from an aquarium, taken it to your place of work and identified it? I ask specifically about the slimy stuff as this is obviously what @Andrew Reynolds has in his tank. But I've also seen a patchy type of BGA, which was more akin to BBA in form but was blue-green in colour. According to Aquasabi, "Quite often, slime algae belong to the genus Oscillatoria (filamentous cyanobacteria)". This is supported by Paul Krombholz at The Krib (remember that?) who says:
"They used to be called bluegreen algae, but cyanobacteria is being pushed as the better name because it draws attention to the fact that they are not related to other algae, but are large, photosynthetic bacteria. Some of them have a bluish pigment in addition to chlorophyll. There are some species that can fix nitrogen, but the ones that take over aquaria are usually varieties of Oscillatoria, which does not have heterocysts, and I assume it does not fix nitrogen".
So, perhaps what we have/don't have in our tanks is not Microcystis aeruginosa after all. No less than 22 years ago, George Booth (also at The Krib) wrote:
"We had a mild problem with blue-green algae growing below the gravel line along the front of our acrylic tanks. I would suppose conditions there are good: light being channeled in via the plastic, no water movement, low oxygen, available nutrients (?)".
The plot thickens.