Digital LSI Calculator
Calculate your LSI in a few taps with this online tool. There’s nothing to line up by hand, and no guessing about where your water stands.
What is the LSI calculator?
The Langelier Saturation Index, or LSI, is a simple read on how balanced your pool or spa water is. It also happens to be one of the biggest factors in keeping your surfaces and equipment from wearing out before their time. Input your numbers into the calculator and it tells you plainly whether the water is corrosive, scale-forming, or sitting right where it should be.
Staying on top of your LSI pays off. Balanced water helps your plaster, tile, pumps, and heater last longer, so you run into fewer surprise repairs from corrosion or scaling down the line. It also helps keep water balance in check for optimal swimmer comfort: less of the skin and eye irritation that can cut an afternoon in the pool short.
What the reading tells you
- Corrosive Eats at plaster and corrodes metal
- Balanced Right where you want it, nothing to do
- Scale-forming Cloudy water and crusty deposits
It protects your plaster and tile, helps pumps and heaters last, cuts down on repairs, and keeps the water comfortable.
What Is The Saturation Index?
The Langelier Saturation Index (LSI) tells whether water is scaling or corrosive and helps find the perfect balance.
What Does The LSI Mean?
| SI | Condition | Risk |
|---|---|---|
| −0.30 or lower | Corrosive | Pitting or etching of plaster Metal corrosion |
| −0.30 to +0.30 (close to zero) | Balanced ✓ | Ideal range No treatment needed |
| +0.50 or higher | Scaling | Cloudy water Scale on surfaces |
Water Temperature And LSI
Water temperature can significantly impact water balance, so it's important to check the LSI in the summer and winter and after refilling the pool.
Borate and Carbonate Alkalinity
Borates are often added to improve pH stability and water clarity. However, borates also contribute to buffering capacity in a similar way to carbonates. Because standard total alkalinity tests measure both, the reported alkalinity value can be higher than the carbonate alkalinity used in the LSI calculation.
If your water contains borates, enable the "Uses Borate" option in the configuration and enter the current borate level. The calculator will adjust the total alkalinity by removing the borate contribution, allowing the LSI to be calculated using the true carbonate alkalinity.
As a result, the LSI calculated with borates enabled may differ from the LSI calculated without borate adjustment.
How To Adjust LSI
Adjusting TA affects pH so retest after each change.
2. pH — Second priority.
3. Calcium Hardness (CH) — Adjust last.
After you've made the necessary adjustments, retest to see if the water is balanced.
Chemical Adjustments Reference
Target Ranges
| Parameter | Pool | Spa |
|---|---|---|
| pH | 7.4 – 7.6 | 7.4 – 7.6 |
| Total Alkalinity | 80 – 120 ppm | 80 – 120 ppm |
| Calcium Hardness | 200 – 400 ppm | 150 – 250 ppm |
| CYA (Stabilizer) | 30 – 50 ppm | Not recommended |
| Borate | 30 – 50 ppm | 30 – 50 ppm |
| TDS | < 2000 ppm | Dump regularly |
| Temperature | 78°–82°F (25–28°C) | ≤ 104°F (40°C) |
Example
Result: SI ≈ −0.6 → Corrosive. Action required.
Solution: Hold pH and TA constant; raise Calcium Hardness from 50 to 200 ppm (+150 ppm) using Calcium Chloride. The 50 ppm CH was below recommended guidelines — hardness adjustment was the correct choice here.
Your LSI and guidance in seconds
This one is for just about everyone who cares about their water. Pros, techs, and dealers reach for it on the job, educators use it to teach, and plenty of homeowners keep it handy for their own pool. If you want water that stays balanced for the long haul, it was built with you in mind.
Enter your test results
Punch in your latest test numbers, like pH, alkalinity, and calcium hardness. Add the rest if you have them.
Follow the prompts
The calculator walks you through each field, so nothing slips through and there is no guessing.
Get your LSI and next steps
Your LSI value shows up right away, along with plain advice on how to bring the water back into balance.
Make decisions with confidence, not guesswork
Good pool and spa care starts with an accurate water balance reading. Doing that math by hand takes time and it's easy to slip up somewhere in the steps. The digital version runs the calculation for you for faster answers with less room for error.
We built it as one more way to make pool care a little easier. The layout is clear, it guides you through each step, and it takes the guesswork out of reading your water. Best of all, it holds to the same accuracy Taylor has always been known for, so you can trust what it says and act on it.
Calculate LSI easily with a digital Watergram®
For decades, our printed Watergram has been the go-to for working out LSI. The digital calculator brings that same trusted methodology into a faster, easier-to-use format.
Think of it as the printed tool you already know, now available wherever you go.