Do your neighbors have trees? Yards? Where does the water to keep all that green shit alive come from? I'm guessing your 450ppm would save you money in nutes, and you can bypass the softener, surely, somewhere. Did you test the water, or look it up or did someone tell you those numbers? I am asking because I have read a thousand threads like this, but often people find tap water is fine. Otherwise, use Spring water, not distilled...are your plants in soil? Checked your original post, yes soil...so just use tap or spring water, no cal mag needed.The very things that make your water hard are magnesium and calcium! Use the tap, bro.
Also, what about using potassium chloride for your softener? Isn't that supposed to be better for plants? I don't know that bit