I'm guessing you have two external overflows, or two drilled overflows ?
Depending on what they are rated for ~ how much waterflow they can handle ~ you may want to consider adding another pump.
Eliminate the Tee
Run the Mag12 to one end of display tank ( spraybar )
Add another return pump to sump running to other end of display tank ( pump selection TBD on overflow capacity )
Upside:
This would allow you to get rid of the Tee fitting, give you two pumps in the sump, and increase your turnover through the tank and through your sump/filtration.
If one pump goes "belly-up" you're still up and running until you can replace it. Nice back up insurance to have on a large tank.
Downside:
If you select the additional pump, and it's pumping too much water for your overflow(s) to handle - oops - might get wet floor.
Other negative - having two pumps may add some additional heat to the water.
Just an idea