I have had my tank (Evo 13.5) set up for about 4-6 months now and never had cyano, even at the beginning. But I did a small water change and removed about half a pound of macro algae out of the tank and the day after had a decent spot of cyano on the sand. It's been a week and it is just growing and spreading like crazy, what could be causing this. I use RO water and instant ocean reef salt