Pump Configuration

I am in the process of developing my plans for a drilled 120G freshwater tank. It is being converted from salt, and I plan to use an existing sump. (I realize the challenges with a sump and co2, so not looking for input to that point.) I have a fairly simple question relative to plumbing. I plan to use a Magnum 350 deluxe for water polishing, and will have it fed from water in the sump. Should the output from the Magnum go back into the sump where my 1200gph pump will then return the water to the tank, or should I pump from the Magnum back to the tank (which would require a "splitter," for lack of a better term, for the water from the magnum would tie into the return line being fed from the main pump.

The first scenario would be much easier to implement, but I wonder if the water would circulate enough.. I dont want to constantly polish the same water, over and over.Would there be enough flow or turbulence in the pump, as to adequately cycle enough "different" water through the polisher.

Thanks for every ones advice and feedback...