I used to live in NYC, which is renowned for it’s great fish keeping water...I drive to town and get town water for my water changes.
Then I moved upstate and now have insanely hard well water like yours. I rescued a poor cold lone surviving betta from a school project last year, and I mixed my well water with RO in a 25:75 ratio and that brought all the numbers back down to acceptable range. I have RO in the house so that was the easiest no brainer method for me. the fish recovered and lived for almost another year. Unfortunately someone in the house sprayed bug spray near his tank, it got into the water and killed him