If you have no sump. Then there is not that much choice. 
Deltec MCE600 is the best you can get for HOB. 
I have one running now but would rather get a sump and put Tunze in there. 
or something that would give you a lot of air mixing /hr, low on energy consumption, quiet, NOT water level sensitive  and easy to clean 
JMO. 
		
	
		
		
		
		
		
	
		
		
	
	
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