ᐅ Looking for a water treatment system for drinking water (well water, iron/manganese removal)

We get our drinking water in our two-family house from a 40 m (130 ft) deep well. Unfortunately, it contains high levels of iron and manganese (in raw water: Fe 3.6 mg/l, Mn 0.57 mg/l). Over the past 12 years, we have had problems with the fourth filtration system (i.e., the filter performance declines, and the drinking water still contains iron and manganese), with each system costing several thousand euros. All four were/are filter media backwash systems (using potassium permanganate or salt) and worked very well for about a year, then gradually worsened. I have the impression that backwashing is the wrong approach for these concentrations; the filter material gradually clogs and loses its filtering function (just a hypothesis).

Does anyone have experience with such systems and can recommend a solution for system #5?