kaiser, I was concerned about 'back-pressure' too, along with preventing 'Stress fractures' known to be experienced with Mag pumps.

I am using two (2) 1-inch 'T' in the 'Return' line:
a. The 1st 'T' directs flow to the CA Reactor, which has a Ball Value to prevent too much pressure on the CA Reactor.
b. The 2nd 'T' directs flow to the Chiller and is 'unrestricted'.
c. The rest of the main flow hits the SWID, before returning water to the tank.

I figured that the 2nd 'T' line to the Chiller would prevent back-pressure from occurring, but I am not plumber.