I just use the “battery electrolyte solution” available at most part shops. It’s dilute sulfuric acid so if a little gets on you no big deal (but I’d still wash my hands after I was done just as a precaution) and it’s relatively cheap also.
My water is around 500 ppm with a lot of calcium and iron and I normally use 2ml per gallon of the electrolyte solution, and that’s with it straight from the tap, I don’t have an RO system. But since it is straight from the tap I try to do it a day or 2 before hand as it does seem to make some calcium(I’m guessing that’s what it is) fall out of solution and that’s just less unknown stuff going into my soil