once the cyano is established it sort off lives off of nothing. That's why even when people add the GFO media they often still have cyano. Or when you use biopellets and macro and hair algae can't survive but cyano still can.
I feel like I had good results with ZeoZym but it could have just been natural ageing of the tank too. If you have a sponge dying in your system it can kick off a cyano bloom - I think Xenia might do that as well.