Wow, interesting Toby! I have had great success with what I thought was cyano, until now, but maybe it was spirulina. In retrospect, I bet it was spirulina, as I dosed erythromycin, which should wipe out cyano, and it didn't work. ChemiClean, which I had purchased 6 months prior, then never used it for fear of adding chemicals, worked great, but now I'm thinking I may need a microscope. How do you distinguish them and what was your H2O2 regimen?... and you verified it's cyano with hydrogen peroxide? In my experience, Chemiclean does not work against cyano. But it works great against spirulina... which to the naked eye can look absolutely identical to cyano. Only being able to distinguish them apart under a microscope. I had a problem with cyano during my tank cycle. I wiped it out with a hydrogen peroxide dosing regiment. A couple of weeks later it came back. So I dosed again with hydrogen peroxide and it didn't touch it. I finally figured out that it was most likely spirulina... so I tried Chemiclean and it wiped it out in two days.