Iron Filters for Well Water: Air Injection vs Manganese Greensand

Before you shop, get a certified lab panel that reports total iron, ferrous vs ferric iron, manganese, hydrogen sulfide (H2S), pH, and dissolved oxygen. Each of those numbers picks the technology.

Air-injection filters work well when total iron is under about 8 ppm, manganese is under 2 ppm, and H2S is moderate. Above those thresholds, or with very low pH, you need a different system or pre-treatment (often a small chemical feed pump).

An air-injection iron filter draws an air pocket into the top of the tank during each cycle. The dissolved iron (ferrous, invisible) hits the air, oxidizes to ferric (rust-colored particles), and the media bed traps it. The next backwash flushes everything to drain.

This is the dominant whole-house iron technology today because it does not need chemicals, and one tank handles iron, manganese, and most H2S. SpringWell, Aquasana, and SoftPro all sell well-water variants of this design.

Sizing matters more than brand. Match the tank size to your peak flow (count fixtures) and the iron load in ppm. Undersized tanks short-cycle and let iron break through.

Greensand uses a coated media that needs to be regenerated with potassium permanganate (a chemical feed pump and a small tank of solution). It handles much higher iron and manganese loads than air injection, and works at lower pH.

The trade-off is maintenance: you are now responsible for keeping a chemical tank topped up and disposing of spent permanganate. Most homeowners with moderate iron prefer the simplicity of air injection.

Upstream: a 100-micron spin-down sediment pre-filter protects the iron tank from grit. If you have very low pH (below 6.8), add a calcite neutralizer before the iron filter, because iron oxidation needs neutral water.

Downstream: install your softener AFTER the iron filter. Softener resin is destroyed by ferric iron, and the iron filter is what produces ferric iron. If you skip the iron filter and rely on the softener alone, the resin will fail within 1 to 2 years.

If your test also flags bacteria, finish the stack with a UV disinfection unit (covered in its own guide). The order at the point of entry is: sediment, iron filter, softener, UV.