Free tool
LSI calculator
Six readings in, one honest answer out: is your water protecting your plaster, eating it, or coating it? This is the same index used on every one of our service visits.
Your readings
Use a fresh test. Strips are fine to start with; a drop kit or a digital reader will get you closer.
Your LSI
+0.05
Balanced
Water is in balance.
The water is neither dissolving your surfaces nor dropping calcium onto them. This is the range worth holding through temperature swings, which is exactly what shifts on you in spring and fall.
What's driving it
- Nothing stands out as the problem number. Hold these and re-check when water temperature moves 10 degrees.
Carbonate alkalinity after the CYA correction: 74 ppm. That's the number the index uses, not the total alkalinity on your test strip.
Why this number matters more than any single reading
A pool can have textbook pH and still be dissolving its own plaster.
It's the whole picture
pH, temperature, calcium, alkalinity and CYA all pull on the same balance. Chasing one at a time is how pools end up etched with a perfect-looking test slip.
Temperature moves it for free
Water that's balanced in August can drift aggressive in January without anyone touching a chemical. That's why cool-season targets differ here.
The damage is permanent
Etched plaster and scaled tile don't reverse with chemistry. Balance is cheap; resurfacing and calcium removal are not.
This calculator is an estimate built on standard saturation-index math and is meant to help you understand your water, not to replace a test at the pool. Borate levels, unusually high dissolved solids and bad test data will all shift the real number.
Want these numbers handled for you?
Weekly service includes a digital reading of every core level and an LSI check on every visit, sent to you after we leave. Quotes follow an on-site test and a look at your equipment.