In my tank over 24 hours it swings between 7.9 and 8.35. The low value is the night time. The tank is about 6 ft from the deck door and the door stays partially open overnight summertime. 
If you do just a test, it depends a lot when you do it and if you don't like the value, what do you do with it? 
		
	
		
		
		
		
		
	
		
		
	
	
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