Hi Ryan: 
Each GFCI is rated for 15amp - enough to hook a few pieces of equipment to it with a powerbar.  Separate the equip so that in case there is a trip with one of the circuits, equipment plugged in the other circuit will still provide your main tank with water circulation and heat. 
For example: 
GFCI #1 - one of your light units, one of the heaters, skimmer and return pump. 
GFCI#2 - the other light unit, heater#2, powerheads 
 
So if GFCI#1 trips when you are not at home - your tank will still have some circulation from the powerheads until you come home.  Vice versa, if GFCI#2 trips, the return pump will provide the circulation.      
 
If you are not comfortable to replace the original circuit with a GFCI unit, you can get a GFCI extension cord.  Revy/Rona has one for about $45 -rated 15A/1800W. 
 
Hope this helps 
		
	
		
		
		
		
		
	
		
		
	
	
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