What water balance means
Balanced pool water is neither hungry for minerals nor overloaded with them. Pool pros measure this with the Langelier Saturation Index, or LSI.
It combines your pH, total alkalinity, calcium hardness, water temperature and dissolved solids into one number. A reading near zero means the water is stable.
A negative number means it's corrosive and will try to pull calcium out of plaster and grout, and metal out of heaters and ladders.
A positive number means it's scaling and will drop calcium on tile, in your salt cell and inside your heater.
Chlorine and cyanuric acid (CYA, also called stabilizer) don't change the LSI much, but they decide whether your pool stays clean.
CYA protects chlorine from the sun, and the more CYA you have, the more chlorine you need to keep algae away. The calculator sets your minimum chlorine from your CYA reading for that reason.
Ideal ranges we use
| Reading | Range | Source |
|---|---|---|
| Free chlorine (FC) | 5% of your CYA or 3 ppm, whichever is higher | MAHC webinar, NACCHO (5% of CYA) |
| pH | 7.4 to 7.6 (7.2 to 7.8 acceptable) | Maryland COMAR |
| Total alkalinity (TA) | 80 to 120 ppm | Maryland COMAR (60 to 180 allowed) |
| Calcium hardness (CH) | 200 to 400 ppm plaster or pebble; 150 to 250 ppm vinyl or fiberglass | Within COMAR's 150 to 400 ppm |
| Stabilizer (CYA) | No higher than 90 ppm (30 to 50 ppm is a common target, an estimate) | CDC Model Aquatic Health Code (90 ppm cap) |
| LSI | −0.3 to +0.3 | Maryland COMAR (±0.5 acceptable) |
Why Las Vegas pools drift out of balance
Southern Nevada tap water is hard. The Las Vegas Valley Water District reports total hardness around 280 ppm, with calcium around 75 ppm of that, so every top-off adds minerals.
In summer, evaporation can take inches of water out of a pool each week, and the minerals stay behind.
That's why so many Las Vegas pools sit high on calcium and end up with white crust at the waterline, a scaled salt cell or cloudy water.
Heat makes it worse: warmer water pushes the LSI toward scaling, so a pool that tests balanced in January can scale in July with the same numbers.
Summer heat and strong sun also burn through chlorine faster, and stabilized chlorine tablets keep adding CYA. Over a season, CYA can climb until normal chlorine levels stop working.
Once calcium or CYA gets too high, chemicals can't bring it back down. The fix is replacing some of the water, which is part of why drains and acid washes are common here.
How to use the results
Fix alkalinity first, then pH, because alkalinity holds pH in place. Then adjust calcium and stabilizer, and add chlorine last.
Big doses are split in half: add the first half, let the pump run, retest, and only add more if you still need it. Test strips can be off by a fair amount, so a drop test kit gives better numbers to work from.
If your results show high calcium, high CYA, or water that's badly out of balance, that's usually a job for a partial drain or a service visit, not more chemicals.
Our weekly pool service keeps chemistry in range every visit, and a pool drain or acid wash resets hard water.
You can also read more in our high calcium guide and when to drain and acid wash.
Frequently asked questions
What is LSI and what number should my pool be?
LSI, the Langelier Saturation Index, combines pH, alkalinity, calcium hardness, temperature and dissolved solids into one number. Between −0.3 and +0.3 is balanced. Below that the water is corrosive and can etch plaster and damage metal parts; above it, the water tends to form scale.
Why is Las Vegas pool water so hard?
Las Vegas tap water comes mostly from the Colorado River and is naturally hard. The Las Vegas Valley Water District reports total hardness around 280 ppm. In a pool, evaporation removes water but leaves minerals behind, so every top-off adds more and calcium climbs over time.
How often should I test my pool water in Las Vegas?
Test chlorine and pH at least once or twice a week, and more often in summer heat. Check alkalinity, calcium and stabilizer about once a month, and always retest after adding chemicals.
What order should I add pool chemicals in?
Adjust total alkalinity first, then pH, then calcium and stabilizer, and add chlorine last. Add one chemical at a time with the pump running, never mix chemicals together, and retest before adding the next.
Why is my pool chlorine dropping so fast in summer?
Sunlight breaks chlorine down, and hot water and swimmers use it up faster. Stabilizer (cyanuric acid) protects chlorine from the sun, but too much stabilizer makes chlorine less effective. Keep stabilizer in range and test chlorine more often in hot months.
How do I test my pool water at home?
Use test strips or a drop test kit. Dip a strip and match each pad to the color chart, or fill the kit's tubes with pool water and add the drops as the kit's instructions say. A drop kit is usually more accurate than strips. Test before adding anything, and again after.
Is it safe to swim right after adding chemicals?
Wait until a retest shows your water is back in range, and follow the product label for how long to wait before swimming. Run the pump while chemicals mix in, and keep swimmers out until then.
When should I call a pro instead?
Call a Licensed pool pro if calcium or stabilizer is high, since those need a partial drain, or if the water stays cloudy or green, you see scale or etching, or you aren't sure how to handle the chemicals safely. Our weekly pool service keeps chemistry in range, and an acid wash resets hard water.
Sources (9)
- EPA: Trichlor 3-inch tablet label (Reg. No. 45458-18)
- PHTA: Pool & Spa Operator Handbook, Water Chemistry Adjustment Guide
- Indiana Department of Health: Pool chemical adjustment chart
- CPO course: Dose chart (practice questions)
- NACCHO: MAHC webinar, January 2018
- CDC: Model Aquatic Health Code
- Maryland COMAR 10.17.01.45: Pool water balance rules
- Wojtowicz (Journal of the Swimming Pool and Spa Industry): Factors affecting the saturation index
- LVVWD: Las Vegas Valley water quality summary
The label on your product takes precedence.