Iron in Well Water: Softener, Iron Filter or Both?

The short answer

A softener's resin removes dissolved (ferrous, clear-water) iron along with hardness, but oxidized red iron fouls it. Nelsen notes most softeners are rated for about 2 ppm of ferrous iron, and Penn State Extension recommends softeners for iron only below 5 mg/L with pH above 6.7. Above that, or with red water or a sulfur smell, an iron filter goes ahead of the softener.

Reading the test

Iron and the softener
Dissolved iron	What to do
Up to 2 ppm	Most softeners handle it; add 4 gpg per ppm when sizing
2 to 5 ppm	Only a softener whose maker states an iron rating at or above it
Over 5 ppm, red water or rotten-egg smell	Iron filter first, then the softener

Iron filter types

Air injection, such as the iSpring WCFM400K: an air pocket oxidizes iron and sulfur, then backwashes it out; no chemicals.
Media filters, such as the iSpring WCFM550K: oxidize and trap iron on a media bed; check pH and oxygen limits.
Cartridges, such as the Home Master CFRFFE-20BB: drop into a 20-inch big housing and are replaced when spent.

Manganese and pH

Manganese often travels with iron and stains black. Penn State notes greensand and similar oxidizing filters suit combined iron and manganese of about 3 to 10 mg/L; Birm needs pH of at least 6.8 for iron and 7.5 for manganese.