Depending on how far the water has to pump, you will not get all 1200 gph
, but the mag 12 is pretty strong up to 5 feet. I use two of them, one for return and one for my skimmer. I have a SCWD on my return as well and it functions fine. I have had to take it off before and clean it with hot water and vinegar. Other than that it has been fine. Post some pics, I am looking to get my 5 MJ-1200's out of the tank and replace them with a closed loop, so I am really interested when people get these things to work well.