I have a CPR hang on the back fuge that is now sitting empty in the garden (anyone want it for free?) that seemed especially good for cultivation of cyano. The problem is a refugium has all the right conditions for its growth.
The usual "treatment" is erythromycin. If red cyano is endangering your corals and stuff like that, it might be worth it, as it seems to have little effect on the biological filter. But like any antibiotic, it should be used as a last resort. With good circulation in the aquarium, the cyano should remain confined to the refugium.
The erythromycin won't heart macroalgae, because macroalgae is eukaryotic, and antibiotics will for the most harm only kill procaryotic organisms like bacteria and cyanobacteria.