I am having the same problem in my system with cyano, although it hasn't killed anything, yet. I did turn off my lights for 60 hours straight, and this knocked the cyano down drastically, but not completely. The 60 hours without light had no ill effect on my corals or anemones.
I am planning on a 3 day complete black out shortly to completely get rid of the problem. This means you need to completely cover your tank with blankets to ensure no light gets in. There has been a few threads on
www.reefcentral.com on this issue and this has been where I have done my research on how to fix this problem.
You would have had a problem that started the cyano and you could have fixed it, but once it has established, you need to do a 3 day blackout to get rid of it. I would get rid of any media in the canister filter, as this may be one of the reasons this problem started. I have also added extra flow, lowered feedings and changed out my bulbs. None of these affected the cyano at all, and it continues to get worse all the time.
I am planning on doing my 3 day blackout the weekend of September 10 to 13th. I can let you know how it goes if you want to see how mine turns out before you give it a try.