What the checker does
A test kit gives you numbers. This turns them into answers: which readings are fine, which are off and by how much, and which one to deal with first. Each problem links to the calculator that works out the fix, with your numbers already filled in.
Free chlorine and pH are the only required readings, because they matter most from day to day. Add alkalinity, stabilizer and calcium when you have them. The check gets more useful with each one, and the stabilizer reading changes what counts as enough chlorine.
How the score works
The score out of 100 is a summary, not a measurement. Each reading is weighted by how much it matters from day to day:
| Reading | Weight |
|---|---|
| Free chlorine | 35 |
| pH | 25 |
| Total alkalinity | 12 |
| Stabilizer (CYA) | 13 |
| Calcium hardness | 8 |
| Salt (salt pools only) | 7 |
Each reading earns 100% of its weight when in range, 60% when slightly off, 25% when out of range and 0% when it needs fixing first.
Readings you leave blank don’t count either way. Two rules stop the score from hiding a real problem: if anything needs fixing first, the result is capped at Poor (49 or below), and if anything is out of range it can’t rise above Needs attention (74). Otherwise, 90 and up is Excellent and 75 to 89 is Good.
So treat the score as a quick read, and the list of readings as the real answer.
The ranges we use
These are common homeowner targets, the same ones our other calculators use. The two CDC figures, a 1 ppm chlorine minimum and pH 7.2 to 7.8, are public-health recommendations. The rest are guidance, and your equipment or surface manufacturer may give different numbers.
| Reading | In range | Flagged |
|---|---|---|
| Free chlorine | Depends on CYA. At 40 ppm CYA: 4–6 ppm, minimum 3. Salt pool at 70 ppm CYA: 5.5–8, minimum 3.5. | Below the minimum is the most urgent problem the checker can find. |
| pH | 7.2–7.8 | Below 7 or above 8 is treated as urgent. |
| Total alkalinity | 60–120 ppm | Below 40 or above 180 is out of range. |
| Stabilizer (CYA) | 30–50 ppm; salt pools 60–80 | Above 100 is out of range. Below 20 is flagged for outdoor pools. |
| Calcium hardness | Plaster 250–450 ppm; vinyl or fiberglass 150–400 | Plaster below 150, or any pool above 1,000, is out of range. |
| Salt (salt pools) | 2,700–3,400 ppm, or your generator's range | Below 2,400 or above 4,000 is out of range. |
Free chlorine is the one that keeps the water sanitized. Its target moves with your stabilizer, which is why the checker asks for CYA: 3 ppm is plenty with no stabilizer and not enough at 50 ppm. If you leave CYA blank, chlorine is only checked against the 1 ppm floor, and the result says so.
pH decides how well that chlorine works. Above 8.0 most of its strength is gone, which is why the checker treats that as urgent.
Alkalinity steadies pH. When it’s high, pH keeps creeping up; when it’s low, pH swings with every dose.
Stabilizer and calcium change slowly. They’re rarely the first thing to fix, but a high stabilizer reading raises the chlorine you need every day, and low calcium slowly damages plaster.
When something is out of range
The checker lists problems in the order to fix them. Chlorine below the minimum always comes first, because until it’s fixed the pool isn’t reliably sanitized. After that it follows the usual order: alkalinity, then pH, then chlorine, because alkalinity changes how pH responds and pH changes how well chlorine works. Stabilizer, calcium and salt can wait until those are steady.
Fix one reading at a time with the pump running, and give each chemical time to mix before adding the next. Never add chlorine and acid together.
When to retest
- After a correction: retest pH or chlorine about an hour after it has circulated; alkalinity after a few hours; stabilizer after about a week, because granules dissolve slowly.
- During a shock: test chlorine every few hours, and wait until it’s back below shock level before trusting a pH reading.
- Routinely: chlorine and pH a few times a week in swimming season, alkalinity weekly, stabilizer and calcium every few weeks. After heavy rain, a crowded weekend or topping up with a lot of fresh water, test everything.
For what each test number means in more depth, read pool chemistry for beginners. If the water is green or cloudy even though the numbers look fine, the shock calculator is the next step.
Assumptions and limitations
- The score is PoolOwl's own weighting of common homeowner ranges, not an industry standard. Two pools with the same score can have different problems, so read the individual results.
- It can't detect germs, algae starting to grow, metals or phosphates, and a good result isn't a guarantee the water is safe to swim in.
- Results are only as good as your test. Strips and drop kits read in steps, and very high chlorine can make pH tests read falsely high.
- Ranges are for residential pools. Hot tubs need different targets, and public pools follow their state code.
Common questions
Does a good score mean the pool is safe to swim in?
No. The checker only looks at the numbers you enter. Water can test well and still have a problem a home kit can't see, and a test taken this morning doesn't describe the water after a busy afternoon. Keep chlorine at the right level for your stabilizer and retest often.
Why does my chlorine show as low when it's 3 ppm?
Because of your stabilizer (CYA). Stabilizer protects chlorine from sunlight but also holds most of it in reserve, so the more CYA you have, the more free chlorine you need. At 50 ppm CYA the minimum is about 4 ppm.
Can I use test strip results?
Yes, but treat them as approximate. Strips are fine for a quick check of chlorine and pH. For stabilizer and decisions like draining water, a drop-based kit is more reliable.
Sources and methodology references
- Home pool and hot tub water treatment and testing, US Centers for Disease Control and PreventionFree chlorine at least 1 ppm in pools; pH 7.2–7.8.
- Pool School (chlorine/CYA chart and methods), Trouble Free PoolHomeowner guidance relating free chlorine targets to CYA: minimum about 7.5% of CYA.
- APSP-11, the gold standard for water quality, AQUA MagazineSummarizes ANSI/APSP/ICC-11 limits, including calcium hardness of 150–1,000 ppm for pools.
- Common Interferences in Pool and Spa Water Testing, Pool & Hot Tub Alliance (PHTA)High chlorine (usually above 10 ppm) produces falsely high pH readings.
Published October 5, 2026. Results are estimates. See how our calculators work.
Spotted a wrong result or an outdated source? Report a problem with this calculator.
Related tools
- Chlorine calculatorSee how much chlorine to add to reach the right free chlorine level for your pool's stabilizer, in ounces, gallons or pounds of the product you actually have.
- pH calculatorFind how much acid lowers your pH, or how much soda ash raises it. The dose comes from a water-chemistry model that accounts for your alkalinity.
- Alkalinity calculatorRaise alkalinity with the right amount of baking soda, or lower it safely with acid and aeration. The total acid and a safe first-round dose are worked out for you.
- CYA (stabilizer) calculatorGet the stabilizer amount to raise CYA, or the share of water to replace to lower it, plus the free chlorine level your new CYA calls for.
Related guides
- Pool Water Chemistry for Beginners: What Each Test Number MeansWhat free chlorine, pH, alkalinity, CYA, calcium hardness and combined chlorine actually tell you, which ones matter most, and what order to fix them in.Read the guide (4 min)
- Cyanuric Acid (Pool Stabilizer): How Much You Need and Why It MattersStabilizer stops sunlight from destroying chlorine, but it also raises the chlorine level your pool needs. How CYA works, good levels, and how to raise or lower it.Read the guide (3 min)
- How to Lower Pool pH, and Why It Keeps Going UpWhy pool pH keeps rising, how to lower it safely with muriatic or dry acid, the mistakes that make it harder, and when to raise it instead.Read the guide (3 min)
- How to Shock a Pool, Step by StepHow to shock a pool so it actually works. When it's worth doing, which product to use, how to hold the level, and the overnight test that tells you you're done.Read the guide (4 min)