TL;DR
Rising conductivity and sodium leakage from a DI column means the cation or mixed-bed resin is exhausted. Regenerate if the system is designed for it; replace the resin if it is a single-use or unregenerable mixed bed.
What you might see
- DI system conductivity rising above limit at the outlet
- sodium analyzer alarm on the deionized water system
- sodium leakage increasing with flow rate
- resin bed has exceeded rated throughput volume
Likely causes
Cation resin exhausted beyond the rated capacity for the inlet hardness and sodium load
Resin fouled by iron or organic matter reducing effective capacity below the nominal rating
Mixed-bed resin in a non-regenerable vessel reaching end of service life
Inlet total dissolved solids higher than the design basis, reducing the service run between regenerations
Required tools
- In-line conductivity meter or grab-sample kit
- Service volume flow meter or totalizer
- Replacement resin charge or exchange cylinder contact
Safety first
- Spent resin containing absorbed heavy metals or industrial chemicals may require hazardous waste disposal. Do not discard resin without checking your plant waste classification.
- Concentrated acid or caustic regenerant chemicals require chemical-resistant gloves, face shield, and adequate ventilation during handling.
Procedure
- 1
Confirm outlet conductivity and sodium are above acceptable limits using an in-line conductivity meter or grab sample.[1]
- 2
Check the service volume counter on the control head or flow meter. Compare the volume since the last regeneration to the rated exchange capacity for your resin at the measured inlet hardness.
- 3
If the system is a regenerable cation or twin-tank design, initiate a forced regeneration immediately and monitor the rinse-to-waste conductivity to confirm full resin restoration.
- 4
If the system is a non-regenerable polishing DI vessel, switch to the standby vessel and order a replacement resin charge or exchange cylinder.
Warning: Spent resin from a DI or softening system may be classified as a hazardous material depending on what it has adsorbed from the process water. Follow your plant waste disposal procedure before discarding resin. - 5
Pull a resin sample and inspect for discoloration (brown from iron fouling, black from organic fouling). If fouled, acid cleaning of the cation bed or hot-caustic cleaning of the anion bed may restore capacity.
- 6
Update the service volume log and calculate the actual capacity achieved versus rated. A declining trend confirms resin degradation and the need for a full resin replacement.
Sources
Culligan Marlo MGT / MFT Twin Water Softener / DI System general technical documentation, Culligan
Deionization resin service life, regeneration, and resin fouling, general water treatment references (general)
More guides for Culligan Marlo MGT / MFT Twin
How to diagnose hard water breakthrough on a Culligan Marlo MGT / MFT Twin water softener
Hard water breakthrough means the resin bed has exhausted before regeneration triggers. Check salt level and brine concentration, then verify the regeneration time clock setpoint against actual water usage.
How to fix regeneration failure and a stuck control valve on a Culligan Marlo MGT / MFT Twin water softener
A stuck regeneration valve is almost always a failed drive motor, a stripped cam gear, or debris blocking the valve piston. Verify motor voltage, cam position, and piston movement before ordering parts.
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