That is why I like the tunze ATO.  It has an upper float valve that will prevent the ATO from filling if it is over a certain level.  I have also combined this with a 10 gallon resevoir that shouldn't kill anything even if everything was dumped into my system.  The only problem is I only get about 5 days before my resevoir is empty so someone does have to fill it when I go away for a week. 
 
Sorry for your loss. 
		
	
		
		
		
		
		
	
		
		
	
	
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