Look into retro fitting recirculation pumps. You don’t necessarily need access to the plumbing behind a wall and can add a loop under a sink in your bathroom. Ask This Old House has quite a few videos on the subject: https://youtu.be/KdA_gfau1s4

There’s citric acid based softeners as well like nuvoh2o https://nuvoh2o.com/

Not sure how it affects septic systems though.