I've only ever seen 3 in my tank since I set it up and I take no chances. Small wad of epoxy with some crazy glue on one side just for fun. I slap that right over the demon spawn. This is garanteed and for the very rare case it's worth the effort because there's no chance for spread. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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