I'm not exactly sure what causes blue-green algae, but I think it has something to do with excess nutrients. I'm not sure though, definitely somebody else should make a more informed post! 
As far as CO2 goes, Lord Barium, it would probably be beneficial in almost any situation unless there was only a small amount of light.
As far as CO2 goes, Lord Barium, it would probably be beneficial in almost any situation unless there was only a small amount of light.
