I am also having the same issue in my tank. I thought it might be micro bubbles but I turned off my skimmer for a few days and it didn't change anything. 
 
It looks exactly like dust. I haven't been doing anything in the house out of the ordinary so I am not sure what it is.  The tank has been up and running for about 2 months and this just appeared about a week ago. 
		
	
		
		
		
		
		
	
		
		
	
	
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