pH correction dosing — designing an acid or alkali system
Short answer: A pH correction system needs three things — a dosing pump (PVDF for acid), a pH sensor, and a controller that runs the pump from the sensor reading. Alternatively, everything in one unit such as the Edose NEUTRA with pH/ORP sensor (₹25,725).
Manual dosing does not work here, because the pH of the water changes constantly — particularly in an ETP.
Where pH correction is needed
| Application | Target pH | What is dosed |
|---|---|---|
| ETP discharge | 6.5 – 8.5 | Acid or alkali (both directions) |
| RO feed (to prevent scaling) | 6.0 – 7.0 | Acid (H₂SO₄ or HCl) |
| RO permeate (to prevent corrosion) | 7.0 – 8.0 | Alkali / pH booster |
| Boiler feed | 8.5 – 9.5 | Alkali |
| Cooling tower | 7.0 – 8.5 | Acid (usually) |
| Swimming pool | 7.2 – 7.6 | Acid or alkali |
Three ways to build it
1. Simplest — manual dosing
A standard dosing pump at a fixed setting. This works only where the feed water pH is fairly steady.
Cost: NEO 10 LPH PVDF at ₹15,750 for acid duty
Limitation: if the incoming pH shifts, the dose is wrong. This approach does not work in an ETP.
2. Easiest — all-in-one unit
Pump and sensor in a single unit. The sensor measures pH and the pump adjusts its own dose.
| Model | What you get | Price |
|---|---|---|
| NEUTRA/CHLORO with pH/ORP | Pump plus sensor | ₹25,725 |
| NEUTRA/CHLORO PVDF | For acid duty | ₹33,600 |
| DUAL 10 LPH | Two chemicals (acid and alkali) | ₹51,450 |
The DUAL model suits ETP work particularly well, where pH swings both above and below target and correction is needed in both directions.
3. Most control — separate controller
A separate pH controller with a separate dosing pump. This gives you setpoint, dead band and alarms, and the data can go to a panel.
| Item | Model | Price |
|---|---|---|
| pH controller | PO 650 with sensor and relay | From ₹9,975 |
| ETP grade sensor | pH sensor for ETP | ₹23,100 |
| Dosing pump | NEO 10 LPH PVDF | ₹15,750 |
| 4-20mA/RS485 output | Add-on | ₹3,360 |
Special considerations for ETP
ETP water is the most difficult — it carries solids, oil and a constantly shifting pH. So:
- A standard pH sensor fails quickly — an ETP grade sensor is needed (₹23,100)
- Dosing in both directions is required, acid and alkali, because pH swings either way
- Mixing is essential — the water must be properly mixed after chemical injection, or the sensor reads incorrectly
Five points when installing
- Keep the sensor away from the injection point — at least 10 to 15 seconds of flow travel, so that what is measured is fully mixed water
- PVDF throughout for acid — pump, tubing and level switch. See the material guide
- Calibrate the sensor monthly with buffer solutions. Without calibration the controller doses on a wrong reading
- Set a dead band such as 6.8 to 7.2, otherwise the pump switches on and off continuously
- Fit an alarm for pH outside range. A relay output is useful here
Safety — please take this seriously
- Wear gloves, eye protection and an apron — every time
- Add acid to water, never water to acid
- Keep a water tap nearby for eye washing
- Store acid and alkali tanks well apart — mixed together they react violently
- Label every tank clearly with its contents
Three budget levels
| Setup | What you get | Approximate |
|---|---|---|
| Basic | PVDF pump, manual setting, tank | ₹20,000 |
| Automatic (all-in-one) | NEUTRA PVDF plus sensor and tank | ₹38,000 |
| Full control | Controller, ETP sensor, pump, output | ₹55,000+ |
Where a pollution board requirement applies to an ETP, the third option is effectively mandatory, because both records and alarms are needed.
Have your pH correction system designed
Send your application (ETP, RO, boiler), flow and current pH — we will design the complete system and quote it.
💬 WhatsApp par poochhein 📞 9910646957Frequently asked questions
Which chemicals are used for pH correction?
Sulphuric or hydrochloric acid to lower pH, and caustic soda, lime or a pH booster to raise it. On RO permeate a pH booster is normally used because only a small increase is needed.
Can manual dosing control pH?
Only where the incoming water pH is fairly steady. In an ETP the pH changes constantly, so an automatic system with a sensor is the only thing that works; otherwise the dose is alternately too much and too little.
How often should a pH sensor be calibrated?
At least once a month using buffer solutions. Without calibration the controller works from a wrong reading and doses incorrectly. In difficult water such as ETP, calibration may be needed more often.
What safety precautions are needed for acid dosing?
Always wear gloves, eye protection and an apron. Add acid to water and never water to acid. Keep a water tap nearby, and store acid and alkali tanks well apart because they react violently if mixed.
Why will a standard pH sensor not work in an ETP?
ETP water contains oil and solids that quickly foul and block a standard sensor junction. A purpose-built ETP sensor is made to withstand those conditions, which is why it costs considerably more.