To avoid microbubbles you should aim for 3-6x turnover through the sump.  I like 5-6x personally.  Some people have 10x+, but you may experience troubles with microbubbles in the display then.  If you choose a higher turnover through the sump you can add more baffles to it to help with microbubbles. 
		
	
		
		
		
		
			
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				~ Mindy 
 
SPS fanatic. 
			 
		
		
		
		
	
		
		
	
	
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