Hmm, just a thought... how did you acclimate your crabs when you added them to the tank? Did you drip acclimate over the course of a couple hours? If you didn't slowly acclimate them, that is likely the cause of their death rather than some off parameter. 
		
	
		
		
		
		
			
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				Calvin 
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Planning a 29 gallon mixed reef...
			 
		
		
		
		
	
		
		
	
	
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