Example data table
| Scenario | pH | Temp (°C) | TDS (ppm) | Ca Hardness | Alkalinity | Typical risk | Target (mg/L) | Product (mL) |
|---|---|---|---|---|---|---|---|---|
| Soft well water | 7.0 | 20 | 250 | 80 | 70 | Low | 2 | ~19 |
| Moderate hardness | 7.4 | 25 | 600 | 200 | 150 | Moderate | 4 | ~38 |
| Hot greenhouse recirculation | 7.8 | 32 | 900 | 280 | 180 | High | 6 | ~57 |
| Very high scaling risk | 8.2 | 30 | 1200 | 350 | 240 | Very high | 8 | ~76 |
Formula used
- LSI = pH − pHs
- pHs = (9.3 + A + B) − (C + D)
- A = (log10(TDS) − 1) / 10
- B = −13.12 × log10(T(K)) + 34.55
- C = log10(Ca hardness) − 0.4
- D = log10(Alkalinity)
The calculator converts scaling risk (LSI) into a typical target residual active mg/L. It then computes product volume using: mL = (target mg/L × liters × 1/1000) ÷ (%active) ÷ density.
How to use this calculator
- Measure pH, TDS, calcium hardness, and alkalinity from your water source.
- Enter the tank volume you will treat, then confirm units.
- Keep Auto mode for a quick starting dose, or choose Manual if your supplier specifies an active ppm.
- Enter your product strength and density from the label or data sheet.
- Press Calculate, then download CSV or PDF for records.
Water scaling and why it matters
Mineral scale in irrigation systems
Calcium carbonate scale forms when water is supersaturated with minerals and carbonates. In gardens and greenhouses, scale narrows dripper labyrinths, blocks mist nozzles, and reduces distribution uniformity. Flow loss often appears as dry spots, uneven growth, and frequent emitter replacement. Warm water, high pH, and elevated alkalinity accelerate deposition on wetted surfaces and inside injectors.
Using LSI as a practical risk indicator
The Langelier Saturation Index (LSI) estimates whether water tends to dissolve calcium carbonate or precipitate it. Positive values suggest scaling potential, while negative values suggest mild corrosion tendency. This calculator approximates pHs from temperature, TDS, calcium hardness, and alkalinity, then converts LSI into a starting residual target. Treat LSI as screening guidance, not a substitute for full lab interpretation.
Choosing a target residual for inhibitors
Most inhibitors work by threshold control and crystal modification, slowing nucleation and keeping scale soft enough to flush. Higher risk water typically needs a higher active mg/L residual, especially in heated lines or recirculating tanks. If your supplier provides a verified dose range for your product chemistry, use Manual mode and enter that active target to match label guidance.
Injection and mixing best practices
For consistent performance, dose into turbulent flow or a well-agitated tank. Add inhibitor before topping up to improve blending, and keep filters clean to avoid false clogging symptoms. When using fertigation, check compatibility with acids and phosphates, and avoid overdosing that can cause slick deposits. Periodic line flushing and emitter inspection confirm the program is working.
Monitoring and recordkeeping
Re-test water seasonally or after source changes. Track pH, alkalinity, and hardness alongside injector settings and tank volumes. Exporting results to CSV or PDF helps document dose decisions, compare batches, and support troubleshooting. A quick acid flush schedule can complement inhibitors when mineral load spikes unexpectedly midseason. If scaling persists, verify field measurements, review filtration and pressure regulation, and consult a water specialist for additional indices or treatment options.
FAQs
1) What does a positive LSI mean for my drippers?
A positive LSI indicates water that is more likely to precipitate calcium carbonate, increasing the chance of scale inside emitters and fittings. Use it as a risk flag and confirm with field performance and water tests.
2) Should I use Auto mode or Manual mode?
Auto mode is a sensible starting point when you only have basic chemistry data. Use Manual mode when your product label or supplier specifies an active residual or ppm target for your exact inhibitor chemistry.
3) Why does temperature change the dose recommendation?
Warmer water generally increases scaling tendency and changes the saturation pH (pHs) used in LSI. Higher temperatures can raise risk, so programs often require a higher residual or more frequent flushing.
4) My hardness is high, but LSI is low. How?
LSI depends on multiple factors, not hardness alone. Lower pH, lower alkalinity, or cooler temperatures can offset hardness and reduce scaling tendency. Always review the full input set and re-check units.
5) Can I dose inhibitor in a fertigation tank?
Often yes, but confirm compatibility with fertilizers, acids, and phosphates. Mix in the correct order, keep agitation on, and avoid combining products that form precipitates. When uncertain, perform a jar test first.
6) How often should I update my inputs?
Update after any water source change and at least seasonally. If you notice clogging, white deposits, or pressure changes, re-test immediately. Regular monitoring keeps dosing aligned with real field conditions.