Water softener hardness setting: what number to enter (plus iron and manganese math)

Enter the hardness of your own tap water in grains per gallon (gpg), plus 3 to 5 gpg for every 1 ppm (part per million) of iron. Round up to the next whole number, and that's your setting. It beats both the factory default and the average printed in your city's water report.

The number matters because the control head, the valve with the display on top of the resin tank, uses it as a divisor. Enter too little and hard water slips through before the next regeneration, the softener's cleaning and recharge cycle. Enter too much and the softener regenerates early, paying for salt it didn't need.

The manual for the Fleck 5600SXT, a common control valve, spells out the math. The valve divides its capacity, the grains of hardness the resin can hold, by your hardness setting. Then it subtracts a reserve, a cushion of soft water held back, and the result is how many gallons it can soften before regenerating.

City report or your own test?

Your own test wins. A city's annual water report gives one average for a whole system, and many systems blend sources: wells, rivers, reservoirs. The report might say "average 11 gpg, range 7 to 19," while your street gets the 19 gpg source all summer.

Program 11 into that softener and it plans for water about 40% softer than what actually arrives. The resin runs out days before the valve expects, and the hard water goes straight into your water heater. You notice it as spots on the glasses again, a week after you "set everything right."

So test a cold tap the softener doesn't feed, often an outdoor spigot. Or put the softener in bypass, the valve setting that routes water around it. Then run a cold tap for a minute to clear softened water from the pipes. Test, then turn the bypass valve back to Service.

The hardness testing guide compares strips, drop kits and lab tests. If you only have the city report for now, use the top of its range until you can test. If your result is in mg/L or ppm, which are the same thing for water, divide by 17.1 to get gpg and round up. The ppm to gpg chart has the common values worked out.

The number itself: hardness plus iron

On city water, the test result usually goes straight in. On a well, check the lab report for iron first. Clear-water iron, also called ferrous iron, pours out of the tap clear and turns to orange stains after it meets air. A softener removes it the same way it removes hardness, so that iron uses up resin capacity too.

The formula:

Setting = tested hardness in gpg + (iron in ppm x 3 to 5), rounded up

Anywhere in that 3 to 5 range is reasonable. The higher end makes the softener regenerate a little sooner, which gives iron less time to build up on the resin.

A softener handles this iron only up to about 1 to 3 ppm, depending on the unit. The Water Quality Association says a softener needs water with less than 2 ppm of iron to reach its rated efficiency. Above that, or with iron that already comes out red, put a dedicated iron filter ahead of the softener. Then test the water between the filter and the softener, from a sample tap if your plumbing has one, and enter only what's left.

Manganese, the other metal on many well reports, leaves brown-black stains where iron leaves orange. It also uses up resin capacity, so it gets added on top of hardness too. There's no single published figure for how many grains to add per ppm. Use the number in your valve's manual, or ask the manufacturer if the manual is silent.

Test result to setting: six common cases

City water, tap tests at 8.2 gpg (140 ppm), no iron

Enter 9. Round up to the next whole grain.

City report says "average 9 gpg, range 6 to 14", your tap tests at 13.5

Enter 14. Your tap beats the average.

Well, 14 gpg hardness and 1 ppm clear-water iron

Enter 17 to 19. That's 14 plus 3 to 5 for the iron.

Well, 22 gpg hardness and 2 ppm clear-water iron

Enter 28 to 32. With iron at the 2 ppm mark, price an iron filter too, and expect to use a resin cleaner now and then.

Well, 18 gpg and 3.5 ppm iron, with an iron filter ahead of the softener

Enter 18 if the water after the filter tests free of iron. Add 3 to 5 grains for each ppm the filter leaves behind.

Very hard water, tests at 50 gpg

Enter 50. The Fleck 5600SXT accepts settings from 1 to 199, so the valve can take it. Above 30 gpg, though, the Water Quality Association notes that some hardness may leak through. Test the softened water as well.

Household size doesn't belong in this number. Hardness is what's in each gallon, and it's the same whether one person lives there or six. The flow meter in the valve counts the gallons, and household size matters only in the reserve. For the other settings on the screen, see the water softener settings guide and the Fleck 5600SXT settings walkthrough. A timer-only softener has no hardness field at all; the settings guide shows how to set its days instead.

Set too low or too high: what each costs you

Take a softener with 24,000 grains of usable capacity in a three-person home. The family uses about 225 gallons a day, and the water really measures 16 gpg.

• Set too low, at 10. The valve expects 2,400 gallons per cycle (24,000 / 10). The resin is actually spent at 1,500 gallons (24,000 / 16). For the last 900 gallons, about four days of use, the house gets hard water, and it looks exactly like a softener that's stopped softening.
• Set too high. Leave a placeholder of 30 on water that measures 10, and the softener regenerates after using only a third of its capacity. That's roughly three times the salt and three times the drain water, for water that's no softer. You end up hauling 40-pound bags down to the basement far more often than you should.

Too low is the costlier mistake for your pipes and water heater. Too high costs salt. The Water Quality Association calls overtreating water a wasteful practice, and an inflated hardness setting is a version of exactly that.

Is the number working? Test the softened water

Once the setting is in, test a softened tap on the last day before a regeneration, when the resin is closest to spent. If your display shows gallons remaining, that's when the count is near zero. A softener in good health delivers water that tests at or near zero. Anything under 1 gpg counts as soft on the Water Quality Association's scale. Harder right before regeneration but near zero right after? Then the hardness setting is too low or the capacity setting is too high.

Re-test the raw water about once a year on a well, and on city water whenever the utility changes its source. Sometimes the raw hardness hasn't changed, yet hard water shows up earlier each cycle. Then the resin itself may be worn or fouled, which the guide to hardness creep covers.