Do you have a sump?  One of the reasons for having a sump is to have that oil slick drain into the sump, get mixed up into the watrer colum and then be pulled out by the skimmer. 
 
If you don't have a sump then maybe try an overflow box for the skimmer, that will help pull stuff off the water surface. 
 
I think, in time, you will find that the Seaclone is an underpowered skimmer, and I have no idea what black powder is.  Is that a Mark Weiss product???? 
		
	
		
		
		
		
			
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				 -- Tony 
 My next hobby will be flooding my basement while repeatedly banging my head against a brick wall and tearing up $100 bills.  Whee! 
 
			 
		
		
		
		
	
		
		
	
	
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