Nope, no way to force them the decision is theirs.  One difficulty is that a BTA isn't a natural host for a perc, not sure about the black saddle though. My ocellaris clowns hosted the BTA after about a month together. Now they won't leave. 
		
	
		
		
		
		
			
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				Brennan
			 
		
		
		
		
	
		
		
	
	
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