Water softener hardness setting, with iron added the way your manual says

The best water softener hardness setting is your raw water hardness level in grains per gallon (gpg), plus the iron allowance from your softener’s manual. The Whirlpool, WaterBoss and GE (discontinued GXSH40V) manuals all say to add 5 for every 1 ppm of clear-water iron, so a well with 15 gpg of hardness and 2 ppm of iron gets a setting of 25. The number tells the softener how much hardness each gallon carries, so it decides how soon the softener regenerates.

Convert your test result to grains per gallon

Softener controls take hardness in grains per gallon. Lab reports usually give it in mg/L (or ppm) as calcium carbonate, so divide by 17.1. The GE softener manual and Nelsen’s sizing guide both give that divisor.

If the result falls between two whole numbers, round up. The WaterBoss manual says the same for its test strips: if the color sits between two readings, use the higher one. Iron is different: for iron, mg/L and ppm are the same number, and you don’t divide it. If your report lists calcium and magnesium separately, or you’re unsure which line is hardness, our guide to reading well water test results walks through each line.

Add iron the way your manual says

Clear-water (ferrous) iron uses up resin capacity along with hardness, so manuals tell you to add it to the setting. The total is called compensated hardness. The makers don’t agree on how much to add per ppm:

Use your own softener’s factor. Dealer-built Fleck and Clack systems don’t come with one, so ask the seller or use 5, the most cautious of the three.

Only dissolved iron counts. If your water comes out of the tap orange or cloudy, the iron has already oxidized, and the Whirlpool manual says its softener will not remove that kind. Our iron filter vs water softener guide covers where a softener stops being the right tool for iron.

Manganese is not added. None of the manuals we read gives a manganese factor, and the numbers on seller calculators come without a source. If your test shows manganese, follow your manual’s guidance or remove it with a filter first. The WaterBoss manual also advises against potassium chloride when iron or manganese is in the water.

Water softener hardness setting chart

Each cell is raw hardness plus 5 per ppm of iron, the rule in the Whirlpool, GE and WaterBoss manuals. Find your hardness on the left and your dissolved iron across the top.

With a factor of 4 or 3 the numbers come out lower, and the gap grows with iron. At 15 gpg, 2 ppm of iron gives 25 at factor 5, 23 at factor 4 and 21 at factor 3. At 3 ppm it’s 30, 27 and 24.

The far right column and the bottom rows are outside Penn State Extension’s range for softening iron: it recommends a softener for iron only below 5 mg/L of dissolved iron, with hardness between 3 and 20 gpg and pH above 6.7. Past that, an iron filter ahead of the softener is the safer plan.

Why “25” and “30” come up so often

If your softener shows 25 and nobody set it, that’s the factory default, not a reading of your water. The GE, Whirlpool and WaterBoss controls all start at 25 when you open the hardness setting, and the Clack WS1 and Hellenbrand controls start at 20. The number 30 shows up in forum answers because it’s the worked example in the GE and Whirlpool manuals: 20 gpg of hardness plus 2 ppm of iron times 5.

Get your setting from the calculator

The first line of the calculator below, compensated hardness, is the number to enter. Open “more inputs” and pick the iron factor from your manual. The rest of the results size the resin for your household, which is useful if you’re still shopping.

Calculator

Find your compensated hardness

People in the home

people

Water use per person per day

gal

Hardness

gpg

Dissolved (clear-water) iron

ppm

Manganese

ppm

Grains to add per 1 ppm iron5 (Whirlpool and WaterBoss manuals)4 (Nelsen)3 (Hellenbrand H125 manual)

Days between regenerations

days

Salt setting6 lb per ft³, about 21,000 grains per ft³ (efficient)9 lb per ft³, about 26,000 grains per ft³12 lb per ft³, about 29,000 grains per ft³15 lb per ft³, about 31,000 grains per ft³ (maximum)

4 more inputs +

Resin to buy

1.5

ft³

Compensated hardness

15.0

gpg

Hardness removed per day

4,500

grains

Salt setting

6

lb per ft³

Resin capacity at this setting

21,000

grains per ft³

Resin needed (exact)

1.50

ft³

Sold as about

48,000

grains

Salt per regeneration

9.0

lb

Days between regenerations at this size

7.0

days

Salt per month

39

lb

Conservative continuous flow

7.5

gpm

How this works →

What happens if the setting is too high or too low

On a metered valve, the hardness setting decides how many gallons pass before the next regeneration. The Fleck 5600SXT service manual describes the math: the control divides the unit’s capacity in grains by the feed water hardness, then subtracts a reserve. Here is what that means for a 1.5 ft³ softener at the efficient 6 lb salt setting, which holds about 31,500 grains (21,000 per ft³ in the design table our size calculator uses), in a household using 300 gallons a day:

Too high (25 on 15 gpg water) means 67% more regenerations. Each one uses the same salt and sends the same water to the drain, so your salt and regeneration water rise by the same 67%. The water is no softer for it. Our water softener running cost calculator shows what that costs over a year.

Too low (10 on 15 gpg water) means the resin runs out at about 2,100 gallons, but the valve waits for 3,150. Unless a day override forces an earlier regeneration, roughly the last third of each cycle comes through hard. The GE manual lists “hardness setting too low” as a cause of hard water in its troubleshooting table.

On well water, check the hardness setting once a year, because hardness can drift. The GE manual notes it “can change over time, especially in well water”, and the Hellenbrand manual says to set the control to the highest hardness you’ve measured.

Check that it worked

Test after the next regeneration, and again near the end of a cycle.

1. Close the blend valve if your softener has one. GE’s manual lists an open blend valve as a cause of hard water.
2. Draw from a cold tap that runs through the softener. GE’s troubleshooting table also lists sampling from a fixture that isn’t plumbed to soft water, which outdoor taps often aren’t.
3. Run the water for a minute, then dip a hardness test strip and read it right away. If the color falls between two readings, read the higher one, as the WaterBoss manual says.
4. Compare with Penn State’s hardness bands: soft water is under 1 gpg (17 mg/L). A reading at or near zero means the softener is working.
5. Test once more the day before the next regeneration. If the water is soft right after a regeneration but hard by the end, the setting is too low or your raw hardness has risen.

Hot water can lag. The GE manual notes that after a blend valve change it may take several days to notice a difference at the faucets, because the pipes and the water heater still hold older water.

If the water is hard even right after a regeneration, the setting isn’t the problem. Check the salt level, the bypass valve and the blend valve, and look for a salt bridge (a hard crust of salt above the water). These are the first items on GE’s “no soft water” list.

Where to enter it on common valves

For the full Fleck walk-through, including capacity, reserve and brine fill, see our Fleck 5600SXT settings guide.

If you switch to potassium chloride, check your manual first. WaterBoss says to raise the hardness setting by 12% (multiply by 1.12), while the Whirlpool control has its own salt type setting instead.

Next step

If your compensated hardness came out high, check that your softener is big enough for it with the water softener size calculator, and see our guide to water softener grain capacity for what the rating on the box means at your salt setting. Our best water softeners for well water lists each model’s iron and hardness limits, and more guides are in sizing and running costs.