i think it would work, i like your idea,
the combination of the fliuds your dosing will cause precipitation and a higher calcium carbinate build up on the return pump, i believe the fliud is concentrated in your sump and has not properly been diluted by the entire tank volume in water, thus resulting in excessive build up on your return pump impeller.
i would try, introducing one (say alk) on the left going into the power head
then cal going into the right powerhead
you can recieve the same type of build-up on your powerheads!!!!!!!!!!!!!!!!!!
i'm not that, knowledgable on dosing, but i do believe you can use a dosing pump to create interviels between dosing each fluid and it still work like it should
best of luck