When to fit a chlorine meter — free residual chlorine guide
Short answer: Fit an online chlorine meter only when you need a continuous record — packaged drinking water, municipal supply, or anywhere ppm has to be logged for compliance. Everywhere else an ORP controller (₹13,650) or a simple test kit does the job, and costs far less.
The Chlorine Meter CL 850 is ₹25,200, so it deserves a considered decision.
What free residual chlorine is
When chlorine is added to water it divides three ways:
- Chlorine demand — consumed in killing bacteria and oxidising organics
- Combined chlorine — bound to ammonia and similar, with weak effect
- Free residual chlorine (FRC) — what remains available to continue killing bacteria
FRC is the real protection, because it keeps the water safe further downstream, in tanks and pipework.
Target FRC levels
| Application | FRC (ppm) |
|---|---|
| Drinking water (at the tap) | 0.2 – 0.5 |
| Start of a distribution system | 0.5 – 1.0 |
| Swimming pool | 1.0 – 3.0 |
| Cooling tower | 0.5 – 1.0 |
| Ahead of RO (before the membrane) | 0 — must be removed |
Three ways to measure
| Method | Cost | When it is appropriate |
|---|---|---|
| Test kit (DPD tablets) | Under ₹1,000 | Where checking two or three times a day is enough |
| ORP controller | ₹13,650 | Automatic dosing needed, ppm record not required |
| Online chlorine meter | ₹25,200 | Continuous record with ppm required |
When an online meter is genuinely needed
- Packaged drinking water plant — records required for BIS and FSSAI
- Municipal or large supply schemes — public health responsibility
- Hospital water — infection control
- Automatic chlorine dosing with nobody present
- Audit or compliance — where records have to be produced
In these cases take the Chlorine Meter CL 850 (₹25,200). With a 4-20mA/RS485 output (₹3,360) the data can also be logged by a DL-650 datalogger.
When it is not needed
- A small RO plant where chlorine is being removed, not added
- Where a test kit check two or three times a day is sufficient
- A cooling tower, where ORP does the job better and cheaper
- Domestic or small commercial installations
A middle option
There is also a lower cost route — the chlorine sensor (ORP with pH) at ₹10,500. It infers chlorine from ORP and pH together. It is cheaper than a full chlorine meter but does not give exact ppm.
When it suits: where you need control but not a compliance record.
Automatic dosing setups
| Item | Function | Price |
|---|---|---|
| Edose CHLORO with pH/ORP | Pump and sensor in one | ₹25,725 |
| Edose CHLORO with FRC sensor | Doses on measured FRC | ₹70,350 |
| ORP PO 650 plus pump | Separate units, more control | ₹13,650 plus pump |
Why the FRC sensor version costs so much more: it measures free chlorine directly rather than inferring it. Where exact ppm control is required, as in packaged water, that is what is used.
Looking after the sensor
- Steady flow is essential — a chlorine sensor needs constant flow past it; in stagnant water the reading is wrong
- Membrane cap — some sensors have a cap that needs annual replacement
- Calibration — against a DPD test kit, monthly
- pH influence — readings shift with pH, so keep an eye on pH too
The decision, plainly
- Removing chlorine for RO → no meter needed; use SMBS dosing
- Cooling tower or pool → take an ORP controller, cheaper and better
- Records needed for drinking water → Chlorine meter CL 850
- Limited budget but control needed → chlorine sensor (ORP with pH)
Set up chlorine monitoring
Tell us whether you need control or a compliance record, and we will suggest the most economical suitable option.
💬 WhatsApp par poochhein 📞 9910646957Frequently asked questions
What free residual chlorine level should be maintained?
In drinking water at the tap, zero point two to zero point five ppm, and half to one ppm at the start of the distribution system. Swimming pools are kept at one to three ppm. Before an RO membrane chlorine must be zero, because it damages the membrane.
When should an online chlorine meter be fitted?
When a continuous ppm record is required, as in a packaged drinking water plant, a municipal supply or a hospital. Elsewhere an ORP controller or a test kit is adequate and much cheaper.
Which is better, an ORP controller or a chlorine meter?
For control, ORP is better and cheaper because it indicates how effective the chlorine actually is. But if regulations require a ppm record then a chlorine meter is necessary, because ORP does not give ppm.
Does an RO plant need a chlorine meter?
Generally no, because before an RO membrane chlorine is being removed rather than added. SMBS dosing is used to bring chlorine to zero. If chlorine reaches the membrane it can be damaged within weeks.
What maintenance does a chlorine sensor need?
It needs constant steady flow past it, as readings in stagnant water are unreliable. Calibrate monthly against a DPD test kit, and replace the membrane cap annually where fitted.