How do I tell the difference? I've got a tank sitting directly in front of a window with broken blinds, no plants in it. Green stuff is starting to form on the glass. This was certainly expected and I'm not worried about algae but I dont want Cyano. I put my hand in and tried to smear it but there was no effect, it didn't even feel different then the glass. It's also on a decorative castle and a river rock and the back of my filter(think the filter is an HoB model but it's almost completly submerged and only the top is sticking out of the water)