I have a mag 18 return, mp40w, and two K2's. I am not sure what the mag 18 is putting out at the returns as it comes up from the garage. I used a head loss calculator and it put it about 685 but I think it is a little less so if we say it is 650, then total flow is about 5050gph. I have a tunze 6105 with controller that I want to add as well but the flow is a little more direct then I like and I can't find a great place to put it. I want to order the 6205 shroud for it to produce a wider flow from it. That will put me at about 8483gph. I'll have to wait and see. That may be too much imo.