Hardness · calcium and magnesium
Hard water and scale
Understand hardness test results, convert mg/L to grains per gallon, and distinguish actual water softening from scale conditioning.
01 / The decision
What the result can—and cannot—tell you.
Hardness is mainly calcium and magnesium. Conventional cation-exchange softeners remove those ions; many salt-free systems instead aim to change scale behavior and should not be described as producing soft water.
To convert hardness reported as mg/L CaCO₃ to grains per gallon, divide by 17.1. Keep the original laboratory value in the project record.
Sizing should account for people, daily water use, measured hardness, and any manufacturer-approved iron adjustment. Maximum advertised grain capacity is not the efficient operating capacity.
Hardness itself is not the same as sediment, iron, manganese, chlorine, lead, or PFAS. One symptom such as staining or spots is not a complete diagnosis.
02 / Treatment paths
Match the equipment to the measured job.
Ion exchange
A metered cation-exchange softener removes hardness ions and regenerates with salt or potassium chloride. Compare certified efficiency at a stated salt dose.
Scale conditioning
Salt-free products may be considered when the goal is scale management rather than measurable softened water. Keep the claim narrow and ask for independent performance evidence.
Point-of-use treatment
RO can reduce dissolved minerals at one drinking tap but is not a whole-house substitute for hardness control when fixtures and water heaters are the concern.
03 / Wrong turns
What this result does not justify.
- Choosing by the largest grain number without checking the salt dose used to reach it.
- Calling every salt-free conditioner a softener.
- Ignoring peak service flow, pressure drop, drainage, electrical access, and local discharge rules.
04 / Product evidence
Questions for any seller or installer.
- What capacity and salt efficiency are certified at the selected programming setting?
- What is the rated service flow at the published pressure drop?
- Can the control valve be serviced locally, and are replacement parts available?
Next step
Carry the result into the correct equipment guide.
Product rankings are useful only after the treatment scope and exact concern are defined.
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