Im using a Mag 9.5 for my return pump.. It depends on how far you have to lift the water and how much flow you want to have.. Most people use an Eheim or a Mag drive pump. There are others also, if you google it or search through the diy/ equipment forums you should be able to find more info.. My mag 9.5 is rated for 950 GPH
at 0 head.. I will have it about 4 ft down from the DT so that would drop it to about 800 GPH
.. Im also gonna put a valve on it to throttle the flow back as I dont want 800 GPH
going through my sump, want it at around 400-500GPH. I think its better to go with a bigger pump and have to restrict it some rather than not having e big enough pump to do the job..