It really depends on the reactors size not the tank water volume. If the reactor is recommended to use a 69 gph pump then that is what you should use.
Think about it this way WVUReefer, if I was to have this same reactor on a 500 gallon aquarium then think of the pump size I would need to use doing it your way.
The question really is, how many reactors do I need for my said water volume.