Advanced Water Balance Calculator
Example Data Table
| pH | Temp °C | TDS | Calcium | Alkalinity | Approx LSI | Meaning |
|---|---|---|---|---|---|---|
| 7.2 | 25 | 500 | 150 | 70 | -0.50 | Corrosive tendency |
| 7.5 | 25 | 500 | 250 | 100 | Near zero | Balanced tendency |
| 8.0 | 30 | 1200 | 400 | 160 | Positive | Scale forming tendency |
Formula Used
The calculator uses this common Langelier Saturation Index structure:
LSI = pH - pHs
pHs = (9.3 + A + B) - (C + D)
A = (log10(TDS) - 1) / 10B = -13.12 × log10(Temperature °C + 273) + 34.55C = log10(Calcium Hardness) - 0.4D = log10(Adjusted Alkalinity)
Calcium hardness and alkalinity should be entered as CaCO3. A value below -0.30 suggests corrosion risk. A value above +0.30 suggests scale risk. Values near zero suggest balanced water.
How to Use This Calculator
- Enter the measured pH from a reliable water test.
- Add water temperature and select the correct unit.
- Enter total dissolved solids in ppm or mg/L.
- Enter calcium hardness as CaCO3.
- Enter total alkalinity as CaCO3.
- Use pool correction when cyanuric acid or borate matters.
- Press calculate to view LSI, pHs, status, and advice.
- Use CSV or PDF buttons to save the result.
Understanding Langelier Saturation Index
What LSI Shows
The Langelier Saturation Index estimates calcium carbonate balance in water. It compares actual pH with saturation pH. Saturation pH is the point where calcium carbonate is stable. The result helps identify corrosion or scale tendency. It does not replace a full water report. Still, it gives a useful control target.
Why Balance Matters
Low LSI water can dissolve calcium carbonate. It may attack plaster, grout, concrete, metal, or fittings. High LSI water can deposit calcium carbonate. Scale may form on heaters, pipes, filters, tiles, and exchangers. Balanced water reduces damage. It also improves maintenance planning.
Important Input Values
pH has a strong effect on the final index. Calcium hardness and alkalinity also matter. Temperature changes the saturation point. Warm water usually increases scaling tendency. Higher dissolved solids slightly change ionic strength. Each field should come from a fresh test.
Using Corrected Alkalinity
Pools often contain cyanuric acid. Some pools also use borates. These chemicals can affect alkalinity interpretation. The corrected mode subtracts estimated cyanurate and borate effects. This gives a closer carbonate alkalinity estimate. Use standard mode for ordinary water checks.
Reading the Result
An LSI near zero is usually preferred. A slightly negative value may still be acceptable in some systems. A high positive value needs attention. Avoid large chemical changes at once. Adjust one factor at a time. Retest water after mixing and circulation.
Practical Limits
LSI is a prediction method. Real water behavior also depends on flow, surfaces, treatment chemicals, and time. Testing errors can change the result. Use calibrated kits when possible. For industrial systems, compare LSI with professional guidance. For pools, follow local safety rules.
FAQs
1. What is a good LSI value?
A value close to zero is generally balanced. Many users treat -0.30 to +0.30 as a practical control range.
2. What does negative LSI mean?
Negative LSI suggests water may dissolve calcium carbonate. This can indicate corrosion or surface etching risk in some systems.
3. What does positive LSI mean?
Positive LSI suggests water may deposit calcium carbonate. This can lead to scale on heaters, pipes, tiles, or equipment.
4. Should calcium hardness be entered as CaCO3?
Yes. This calculator expects calcium hardness as CaCO3. Using another reporting basis can create an incorrect index result.
5. Is TDS the same as salt?
No. Salt is part of total dissolved solids. TDS includes salts, minerals, metals, treatment chemicals, and other dissolved materials.
6. Why does temperature affect LSI?
Temperature changes calcium carbonate solubility. Warmer water often has a stronger scale forming tendency than colder water.
7. When should I use corrected pool alkalinity?
Use it when cyanuric acid or borates are present. It estimates carbonate alkalinity more closely for pool balance work.
8. Can this calculator replace lab testing?
No. It is a planning tool. Use reliable testing and professional guidance for industrial, commercial, or safety critical water systems.