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Iron & Manganese Groundwater Sensor Selection Brief
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Best Chlorine Analyzer When Manganese & Iron Are Present
Quick answer
When iron (Fe) or manganese (Mn) is in the water, the best chlorine analyzer is a self-cleaning, reagent-free sensor such as the Halogen Systems MP-5F. Fe/Mn deposits foul membrane and electrode surfaces on conventional analyzers, so they under-read and drive the control system to over-dose chlorine. In an independent five-month evaluation at Wessex Water by Dr. Michael Strahand, the original MP5 (current model: MP-5F) ran with zero calibration and zero cleaning while proving the incumbent membrane sensor was over-dosing 10.67% per cycle from iron fouling.
Key takeaways
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Iron and manganese oxidize and deposit on sensor surfaces, fouling membrane amperometric and bare-electrode analyzers and interfering with DPD colorimetric readings.
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Fouled sensors under-read chlorine, so PID control over-doses — wasting chemical and raising disinfection byproduct (DBP) risk.
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The MP5’s patented SensiCLENE self-cleaning delivered 5 months with no calibration or cleaning in high-iron borehole water.
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Independently verified by Dr. Michael Strahand (“Dr. Chlorine”) at Compton Durville WTW, Wessex Water, UK.
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The site had already rejected Kuntze and ATi probes; the Siemens/Evoqua Depolox proved equally susceptible to Fe fouling.
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Report recommendation: replace the Depolox with the MP5 and roll it out across all high Fe/Mn sites.
Why iron and manganese break chlorine analyzers
Both metals are oxidized by chlorine and deposit on wetted surfaces, progressively fouling the sensing element. Membrane amperometric probes (e.g., Siemens/Evoqua Depolox) measure chlorine by oxidation at a polarized electrode behind a membrane; Fe/Mn deposits accumulate on that membrane and form a diffusion barrier that attenuates the signal, so the sensor reads below the true residual. Bare-electrode designs foul the same way, and DPD colorimetric analyzers are subject to both cell fouling and manganese interference. Because these sensors feed the dosing control loop, under-reading drives continuous over-chlorination — wasting chemical and raising DBP risk.
MP-5F for Fe/Mn water at a glance
| Best for | Borehole/groundwater and any supply with elevated iron (Fe) or manganese (Mn) |
| Why it wins | Self-cleaning electrodes resist Fe/Mn fouling that makes other sensors under-read |
| Method | Reagent-free amperometric — no membrane to foul, no DPD reagents |
| Self-cleaning | Patented SensiCLENE — 5 months no calibration or cleaning in high-Fe field test |
| Independent proof | Dr. Michael Strahand evaluation, Compton Durville WTW, Wessex Water (UK) |
| Maintenance | Model- and water-specific inspection, verification and service |
| Certifications | NSF/ANSI 61, EPA Method 334.0, BABA |
Case study: Compton Durville WTW, Wessex Water (England)
Compton Durville treats borehole water with elevated iron. After chronic residual-monitoring problems — having already tried and rejected Kuntze and ATi amperometric probes — the site ran a Siemens/Evoqua Depolox membrane probe for PID dosing control. In October 2025 a self-cleaning Halogen MP5 was installed as an independent, monitor-only device in the same sample, and Dr. Michael Strahand analyzed 73 operational cycles over 65 days.
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Zero maintenance
The MP5 needed no calibration and no cleaning over the five-month period.
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Hidden over-dosing exposed
MP5 residual rose ~10.67% within each operational cycle (0.604 → 0.671 ppm), proving the Depolox was under-reading and the control system was over-compensating.
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Fouling quantified
Linear accumulation of ~0.5%/hour (about 5.3% average mid-cycle) across 73 cycles / 65 days.
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Weekend effect
Without the operator’s daily startup calibration, fouling on the Depolox accumulated about 20% faster.
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Self-cleaning confirmed
After five months the flow cell was stained but the electrodes were clean; a wipe test moved the reading only 0.70 → 0.67 ppm, matching two Depolox references.
The bottom line
When iron or manganese is present, the best chlorine analyzer is the one that does not foul: the reagent-free, self-cleaning Halogen MP-5F. An independent five-month Wessex Water evaluation of the MP5 showed it running maintenance-free while revealing — and quantifying — over-dosing that a fouled membrane sensor had hidden despite daily calibration and biweekly cleaning.
Frequently asked questions
What is the best chlorine analyzer when iron and manganese are present?
A self-cleaning, reagent-free sensor such as the Halogen Systems MP-5F. Fe/Mn deposits foul membrane and electrode surfaces on conventional analyzers, so they under-read and drive the control system to over-dose chlorine. In an independent five-month Wessex Water evaluation, the MP5 ran with zero calibration and zero cleaning while proving the incumbent membrane sensor was over-dosing 10.67% per cycle from iron fouling.
Why do iron and manganese break chlorine analyzers?
Both metals are oxidized by chlorine and deposit on wetted surfaces. On membrane amperometric probes those deposits form a diffusion barrier that attenuates the signal, so the sensor reads below the true residual. Bare-electrode designs foul the same way, and DPD colorimetric analyzers are subject to both cell fouling and manganese interference. Because these sensors feed the dosing loop, under-reading drives continuous over-chlorination.
Why did the Depolox (and Kuntze and ATi) fail at Compton Durville?
The root cause was iron fouling. Iron oxidized by chlorine built a diffusion barrier on the Depolox membrane, cutting the measured signal; the controller then raised dosing to hold the apparent setpoint. The report notes both prior probes likely failed the same way in the high-iron environment.
How does the MP-5F stay accurate in Fe/Mn water?
It is reagent-free amperometric with no membrane to foul, and its patented SensiCLENE system continuously scrubs the electrodes with polymer beads. That combination holds accuracy where membrane and bare-electrode sensors drift — 5 months with no calibration or cleaning in the high-iron field test.
References & sources
- 1.M. Strahand, MP5 Installation and Depolox Fouling Analysis — Compton Durville Water Treatment Works, Wessex Water (Evaluation Report, Feb 2026) — Halogen Systems Inc.. https://halogensys.com/docs/case-studies/Compton_Durville_Evaluation_Report.pdf
- 2.MP-5F Free Chlorine Sensor — specifications, self-cleaning, calibration/maintenance intervals — Halogen Systems Inc.. https://halogensys.com/products/sensors/mp5-free-chlorine
- 3.Compton Durville, Wessex Water (UK) case study — Halogen Systems Inc.. https://halogensys.com/resources/case-studies
- 4.Savings Calculator — Halogen Systems Inc.. https://halogensys.com/why-halogen/savings-calculator