Cannot get rid of cyano!

[Cal_stir]

I tried the blackout, 4 days no light except 1/2 hour a day ambient light to feed the fish, cyano was gone but quickly returned a couple days later and seemed to spread even faster.
Cyano is probably the most resilient, opportunistic thing on this planet and normally we can keep it in check but sometimes something happens and you get a plague.
I am totally against chemical treatments but I have to thank chemiclean, I was getting ready to quit.