I thought I had a lime green cyano on my sand bed, but it turned out to be spirulina algae I think. I did a peroxide test to determine whether it was cyano or spirulina and it did not turn the water green. I was told that Chemiclean would help get rid of it but I am not seeing any results after 48hours. I am in the process now of doing a 30% water change. It is like dust on the sand bed and you can mix up the sand bed and it looks like it is gone, but an hour later you can see it settling again on top of the surface of the sand. My tank is 3 years old and all parameters are good. I am not sure what started it. I do not over feed and do water changes weekly. Any ideas, thoughts or suggestions would be appreciated.