A lot of people use massive return pumps to get good flow in their aquarium. I suggest to stay away from this approach. Ideally, you want the turnover in the refugium to be quite low. This allows you to maximize your natural filtration. Sumps containing only protein skimmers and other mechanical devices can be run at higher flow, but I still don’t recommend ramping up the flow through your sump. Choose a small return pump and use powerheads to increase the water flow inside the display aquarium.