I ran a 4 stage twist in unit and had the same problem that di didn’t last long, I then had something come through my city water and get through my rodi and killed over 10k of high end corals. Only get a 7 stage even after 4 stage I have TDS and sounds like you have a high tds count too. 7 stage is the only way to protect yourself. Your saltwater can only be as good as your rodi and don’t cheap out. I have a 200 gpd 7 stage from bull reef.