A water softener replaces iron, calcium and other things with salt NaCl. Getting a water softener would probably help an RODI unit. But my city water is not great. It is about 140 TDS. It comes out of my RO membrane at 2 TDS and out of the DI at 0. The pressure is not great about 65 psi. I have a 6 stage BRS. Two stages are DI. I like running two in sequence. That way I can fully deplete one, I use color changing resin, and then switch the one in the 2 position to the 1 position and repack the depleted one and put it into the 2 position. My unit is rated at 75 gpd and it might actually do more. I have a 300 gallon tank. I use. 44 gallon brute trash can for RODI storage. I have another for saltwater. I have a third also. All are on casters. For water changes, siphon out about 40 gallons into my first can. When done, I roll over my saltwater and use a pump to push the saltwater into the tank. I roll the old saltwater to the sink and pump it down the drain. I roll the empty saltwater can to the RODI storage. I have tile floors. Pump the RODI into it. Add salt and let a powerhead mix it. I turn on the RODI and it fills in about 12 hours. If I have to, I can do a water change per day without any trouble. Using the waste can for mixing saltwater, I can mix just about 2 batches of saltwater per day, My system, which works for me, might not work in your circumstances. But it isn't that hard.
