I'm so... Confused, so should we stop planting trees and instead enrich our life's with creating cyano bacteria?It likely did, if it was old.
Cyano is nothing to worry about. It's easy to blow off of corals, and will politely fade away once you correct whatever let it flare up.
It's also neat stuff. Billions of years ago, there was little to no oxygen in the Earth's atmosphere. This was fine with most inhabitants of Earth, to which oxygen was toxic. Then cyano started to proliferate, and as you might know, cyano releases oxygen as it goes about its business. Over the course of eons, cyanobacteria filled the atmosphere with oxygen, even more than we have today, and killed off most of the other life on this planet. Anaerobic bacteria is rare now, since it has to hide from oxygen. And, of course, we couldn't exist without an oxygen-rich atmosphere. Also, most life on this planet is thought to be descended from cyano. Say hello to your great-great-great-great-great-great grandparents, largely unchanged since then.