I have been working on setting up a three tank system one common sump, currently I have one up and running on a canister, and am doing water changes manually. I hope this pic comes through. My thoughts are all tanks will overflow into a single manifold that will dump into one of two identical salt mix tanks fitted with heaters, circ pumps and ATO's the water then flows out to the sump through it and back to the tanks each on their own return pumps. The reason for the mix tanks is both for water volume (40 additional gallons) and convenience. Only one mix tank will be operating in the system at a time the other will be drained refilled and mixing fresh saltwater then once a week or so I can do a water change with the flip of four valves then repeat.
Any thoughts are welcome.