Al,you said you had to skim a brown layer off the surface,what kind of surface agitation is there?If there isnt enough agitation from say a pwr head then there maybe a lack of air exchange.You might want to try alittle more flow to get the surface movement. 
		
	
		
		
		
		
			
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Jim
			 
		
		
		
		
	
		
		
	
	
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