I had a TERRIBLE cyno outbreak, sand, rocks, even some coral's started to get covered. I got some phosban, and also some phophate removal sponge that you could cut to size. Also did 75% water changes 4 times in 2 weeks. Come to find out the MH bulbs I had JUST put in, were not producing at the right spectrum, used my friends light measuring device to figure that out(can't remember what it was called) anyways, I put in some new and "better" MH bulbs, and in 2 weeks, it was all almost gone. Of course I did more water changes, fed less, and syphoned out whatever I could. Cyno SUCKS!!! Water temp and flow are also big culprits in cyno. Not sure what you have circulating in your tank, but from what I have read you haven't had cyno probs before, so your water flo is probably fine. Do you check your RODI water for nitrates before you put it in?