Water softener resin tank with its control valve next to a storage tank
Generic photo: రవిచంద్ర (Ravichandra) · CC BY-SA 4.0

Setting softener hardness: converting a lab or city report (mg/L, ppm) to grains per gallon, plus iron compensation

Most residential softener valves are programmed in grains per gallon. Lab and city reports usually give hardness as mg/L (same as ppm) of calcium carbonate. Divide the mg/L number by 17.1 to get gpg and round up. On well water with dissolved (clear-water) iron, add an iron allowance on top; the factor differs by maker (4 or 5 gpg per 1 mg/L of iron), so use the number in that unit's manual.

Cross-checked ~15 min easyBrands: All

Before you start

  • No electrical or pressure hazard in this task; if you open the valve cover to program it, keep water away from the transformer and board.
  • Do not tell a customer the softened water is safe to drink just because it is soft; softening does not disinfect. Well water safety needs its own lab test.

Diagnostic steps

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Setting softener hardness: converting a lab or city report (mg/L, ppm) to grains per gallon, plus iron compensation · OnCall Tech