Peroxide - you guys will think I'm nuts

[KPG007]

I get cyno in one of my tanks as it heats up during the summer. Normally 78 degrees - no cyano. 80 degrees - cyano starts creeping in. What I found was that even when it cools back down to 78, the cyano will still hang around. So I dropped the temperature down to 76 (even as low as 74) and the cyano disappeared! No negative effects on coral or fish. Give that a try before adding chemicals of any kind.