My GE Cafe dishwasher is leaving a brown/dark stain on everything

My GE Cafe dishwasher is leaving a brown/dark stain on everything

My GE Cafe dishwasher (CDT725SSF7SS) has worked wonderfully for 4 1/2 years, but about four months ago started leaving a terrible brown or dark stain on stainless, plastics and ceramics (basically everything). We have not changed detergent (Cascade), items being washed, settings (normal wash, heated dry, use jet dry), city water is the same, so we are at a loss as to what is causing it.