Set the bed and its load, then read the run length before opening the salt ledger. The result stays operational; every quantity can explain its own relationship.
Model 03 · Open to everyone
Valve stageServiceDownflow through resin
Full run capacity250,000 grainsResin bank after regeneration
Daily hardness load120,000 grainsCapacity spent each day
Capacity and regenerationService
Valve sequenceHard water moves down through the sodium resin.
Diagram controlsInspect a live quantity
Supporting readoutsSeven measurementsOpen
Gallons per cycle16,667gal
Annual salt17,520lb
Salt efficiency2,500grains/lb
Operating curveAnnual salt versus dose10.0 lb/ft³ selected
Annual salt vs dose
Drag the plot to set the dose. Longer runs cost salt at falling efficiency.
Reference
How the softener model works
A softener trades salt for hardness. The salt dose sets how much exchange capacity each regeneration buys, capacity against the hardness load sets the run length, and the same dose decides how efficiently every pound of salt is spent. Those three quantities pull against each other, and the room exists to make the trade visible.
The instrument above runs the capacity math live. The governing relationships are written out below.
Total hardness the bed removes per run. The per-ft³ capacity rises with salt dose along the standard SAC resin curve, so a heavier regeneration buys a longer run.
Resin volume
Resin bed volume (ft³)
Capacity per ft³
SAC resin exchange capacity at the chosen salt dose (20,000 to 30,000) (grains/ft³)
Assumes
Standard SAC resin capacity curve, 6 lb/ft³ → 20,000 gr up to 15 lb/ft³ → 30,000 gr.
Run length
Run length=Hardness×Daily useCapacity
Days between regenerations: the capacity divided by how fast hardness consumes it. Capacity over hardness gives gallons per run; over daily use gives days.
Capacity
Exchange capacity per run (grains)
Hardness
Influent hardness as CaCO3 (gpg)
Daily use
Water treated per day (gal/day)
Assumes
No hardness-leakage allowance or days-of-reserve derate.
Salt per regeneration
Salt per regen=Resin volume×Salt dose
Salt consumed each regeneration. Annual salt is this scaled by how often the bed regenerates over the year.
Resin volume
Resin bed volume (ft³)
Salt dose
Salt applied per cubic foot at regeneration (lb/ft³)
Assumes
Salt dose applied uniformly across the bed.
Salt efficiency
Salt efficiency=Salt doseCapacity per ft3
Grains of hardness removed per pound of salt. Leaner dosing wins efficiency at the cost of run length, the central tradeoff in sizing a softener.
Capacity per ft³
Exchange capacity at the chosen dose (grains/ft³)
Salt dose
Salt applied per cubic foot (lb/ft³)
Assumes
Efficiency falls as salt dose rises along the SAC curve.
Worked example
Take the room's default case: 15 grains per gallon of hardness, 8,000 gallons per day of use, 10 cubic feet of resin, and a salt dose of 10 lb per cubic foot.
Capacity per regeneration
250,000 grains
Water treated per run
16,667 gallons
Run length
2.1 days
Salt per regeneration
100 lb
Salt efficiency
2,500 grains per lb
Drop the salt dose in the instrument and watch efficiency climb while the run shortens. Neither answer is free; the room shows the price of each.
Common questions
How much hardness does a softener remove per regeneration?
Capacity follows the salt dose along the standard SAC resin curve: 6 lb of salt per cubic foot buys about 20,000 grains per cubic foot, and 15 lb buys about 30,000. Multiplying by the bed volume gives the total for the run.
How is run length calculated?
Capacity divided by the hardness load. Capacity over hardness gives the gallons one run can treat, and dividing by daily use turns that into days between regenerations.
What is salt efficiency?
Grains of hardness removed per pound of salt. A leaner dose wins efficiency at the cost of run length, which is the central tradeoff in setting up a softener.