Another possibility is that what you have may not be cyano but rather dinoflagellates?  in that case it is a very different treatment. 
  
I used Seachem HO for elevating my PH without raising my KH and it worked well for me to remove all the dino.  It never returned. 
		
	
		
		
		
		
			
				__________________ 
				_________________________ 
More fish die from human stupidity than any other disease...
			 
		
		
		
		
	
		
		
	
	
	 |