I am also having an issue with cyano. My current attack plan is this: I siphoned out as much of it off the sand as I could see. I lost a bit of sand while doing this, but it's okay for now. I am currently on day 2 of 3 days of darkness. My tank is covered with a dark colored blanket (tented over the top to allow for better gas exchange). After I siphoned everything out, I dosed with Chemiclean. I added a powerhead with venturi for good aeration while the treatment is ongoing and to promote good gas exchange as well. Tomorrow evening, I will be doing a 30% water change to remove whatever has died off in the tank. On Saturday, lights will come back on but at a reduced photo period to prevent shocking my corals. In an attempt to prevent a future outbreak, I just ordered a biopellet reactor, and will add that to the tank when it comes in, but in the meantime I will be dosing Dr. Tim's Waste Away to help control my nitrates. I am going to start the biopellets slowly, only 1/3 of the recommended pellets to start. For me, I am pretty sure nitrates are my problem, and possibly over skimming. I've dialed my skimmer back to see if this works as well. My turnover rate is over 60 times per hour...I can't imagine that flow is the problem, but I do notice that the cyano was heavier where the flow is lower. I have been peeking at my tank just to make sure everything is doing ok, and other than a grumpy BTA and some sleeping fish, all seems well even at almost 48 hours dark. I am hopeful that at least for the time being, this treatment will help, but I know that I need to attack the underlying issue, which in my case is most likely excess nutrients. Good luck!