I wouldn't want the hair algae to slow down because of a reduction in light, because then I wouldn't know if I am taking care of the nutrient problem or not. 
 
In your above equation, you will always have light, so if you want no algae, you have to reduce nutrients. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
	 |