The suggested turnover rate of a return pump is often 5x – 10x that of your systems water volume. However aiming for a lower end of the turnover rate, 5x – 7x, is better for the filtration process, resulting it cleaner, clearer water.
Why? Well, if water is being pumped too quickly, the amount of time being spent passing through the skimmer, reactors and UV sterilizer, if installed, may not be long enough for the water to be filtered effectively. By reducing the flow, it will enable the water contact time to be extended, thereby ensuring more of the water is filtered more thoroughly at each passing.
Most return pump for saltwater aquariums are produced as controllable DC. This is handy because it allows the reefer to purchase one at the top end of the gph range, but you have the ability to dial it down with the controller to your desired flow rate.