Soluble and insoluble iron ...

Soluble and insoluble iron in my humble opinion are to be considered foulants for ion exchange resin.  The resin is that binding to the resin may be more or less non-reversible by typical regeneration procedures.  Resin cleaner products are nominally effective, but require system down-time.  It is best to make sure there is no ferrous (Fe2+) iron in solution, and if it is, then it must be oxidized (permanganate/zeolite treatment works best).  Filter media should be watched more carefully and back-washed on Delta Pressure, or a timer.

If the water softeners are pretreatment for an RO system, then extra caution is required to ensure that no particulate (and no soluble iron) makes it through the softeners, as once iron deposits on membranes, any chlorine punch-through will result in blistering of the membrane at the location of iron particles.