everything I've read on cyano is that it's nothing like controlling hair algae and or diatoms. so it's controlled diff, it's more than likely caused by the change in your system from gfo. the additives to battle cyano or redslime neutralize certain acids or are some sort of oxidizer. like sherita said its from a change in your system, so leave everything the way it is and ride it out. stir the sand and manually remove it. vacuuming the sand has helped me might want to try that.