green chromis can be a bit jumpy and leave the tank. Especially if there is only two. They like to chase each other...I have 9 in my tank and they all do this. chromis also have a reputation of just "disappearing". nobody can explain it. 
		
	
		
		
		
		
			
				__________________ 
				Brad
			 
		
		
		
		
	
		
		
	
	
	 |