For how shallow the fusion 20 is it should be fine. Mine is plenty light for my 34g 20"x20". I've actually dialed it down to about 40-50%.  Be strategic when placing coral as the outer areas will receive less light. Works well for me because some of my Lps don't need much light at all.  It's a great light for the price. You can't go wrong. 
		
	
		
		
		
		
		
	
		
		
	
	
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