My guess is one of the heaters is not working anymore. I would recommend using 2 heaters on 2 different breakers in case something ever happened. Its pretty tough to beat an ebo jager heater they will last forever. They have 300w and i imagine larger models. 
		
	
		
		
		
		
			
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				360 gallon sps reef, 180 gal sump, bubble king supermarine 300, 4xmp40Wes, 2 x 6215 tunze waveboxes, 4 ghl mitras
 360 Reef Tank 
			 
		
		
		
		
	
		
		
	
	
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