Yeah the wall is 18" from the back of the tank and is painted white. The 'background' appears a bit different than before because I have 4x54w T5 along the back now so more light is hitting that wall. 
 
I'm back and forth on the look... I love how the tank seemingly has no back. The powerheads look like they float on ocean. But when I view my corals from th back and look into the dark room in front the 'background' seems black and the colours pop so much more. 
 
I'm likely going to buy a king-sized black bedsheet and pin it to the wall so I can revert if I want. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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