I had the cyano
problem. what I ended up doing was using a treatment that my LFS
had me do. Very well known establishment and very trusted. I think it was Myracin. But, within 3 days, the cyano
was gone. I sucked it off the sand and netted what I could. Shut the skimmer off and carbon filter but kept the sump running. In 3 days did a water change, and started up skimmer and carbon filter, and havent had the problem since. He thinks it might have been the sand. But, it was safe for the fish, inverts etc.