How much throughput a cation/softener resin bed can treat before its exchange capacity is exhausted and regeneration is required — a straight hardness-load mass balance, the same run-length figure DM plant operators schedule regeneration shifts around.
Verified against published standard
Resin Bed & Raw Water
Exchange capacity is the resin manufacturer's rated figure for the specific resin and regenerant dose in use — it varies by resin type/age and regenerant level, so use the vendor datasheet or your own titration result rather than a generic assumed value.
Enter resin bed and raw water data to calculate.
About This Calculation
A cation/softener resin bed removes dissolved hardness (calcium and magnesium, expressed as an equivalent CaCO₃ concentration) from raw water until its exchange sites are used up, at which point it must be regenerated with acid or brine before it can continue. Run length before that point is a straightforward mass balance: how much hardness the resin can hold in total, divided by how fast raw water is delivering hardness to it — the same number real DM plant operators use to schedule regeneration shifts.
Frequently Asked Questions
Why is hardness expressed "as CaCO₃" rather than as calcium and magnesium separately?
Expressing all hardness-causing ions on a common CaCO₃-equivalent basis (using each ion's own equivalent weight) lets calcium, magnesium, and the resin's own exchange capacity all be added and compared on one consistent scale — this is standard water treatment practice specifically so a single hardness number and a single resin capacity number can be used together in one mass balance.
Why does real practice regenerate before the resin is fully exhausted?
Hardness leakage (a small amount of hardness passing through untreated) rises progressively as the bed approaches full exhaustion, rather than staying at zero right up to a hard cutoff — real DM plants set a conservative throughput or a hardness leakage alarm well before theoretical exhaustion specifically to avoid feeding hardness downstream into the boiler, where it directly drives the scaling this whole treatment train exists to prevent.
Does a higher raw water hardness always mean proportionally more frequent regeneration?
Yes — run length is inversely proportional to raw water hardness at a fixed flow rate, so a seasonal or source change that doubles raw water hardness will, all else equal, roughly halve the resin bed's run length between regenerations, which is exactly why raw water quality monitoring feeds directly into regeneration scheduling, not just a fixed calendar interval.