How to Test Your Pool Water

Applies to: Home in-ground and above-ground pools using chlorine or a salt chlorine generator; test strips, liquid drop kits and digital testers.

How often to test

CDC recommends testing chlorine and pH at least twice a day, and more often when the pool is busy.^[1]

PHTA's weekly checklist includes a fuller test of chlorine, pH, alkalinity and other levels.^[2]

AquaChek advises extra tests after a party, after animals have been in the pool, after heavy rain and after fertilizing. It also suggests testing 24–48 hours after adding chemicals so you can rebalance accurately.^[3]

Taylor suggests testing at roughly the same time each day, and says morning is usually ideal, before strong sun starts breaking down sanitizer.^[4]

What to test and why

• Free chlorine: CDC recommends at least 1 ppm in pools, or at least 2 ppm if you use cyanuric acid or stabilized chlorine. CDC's pool guidelines add that the typical range for chlorine is 1-4 ppm, and to follow the manufacturer's instructions for your product. AquaChek explains that total chlorine is free plus combined chlorine, and combined chlorine is used up and no longer sanitizes.^[1][3][5]
• pH: CDC recommends 7.0–7.8. As pH rises, chlorine gets worse at killing germs.^[1]
• Total alkalinity: AquaChek says it buffers your water against sudden pH changes. PHTA notes it is usually measured with test kits or strips.^[3][6]
• Calcium hardness: Taylor explains that total hardness counts both magnesium and calcium, but only calcium hardness matters for water balance, so check which one your kit measures.^[4]
• Cyanuric acid (stabilizer): AquaChek says it helps chlorine hold up in the sun, but levels that are too high make chlorine less efficient.^[3]
• Salt, for salt-chlorine pools: PHTA says different generators need different salt levels, so follow your maker. Latham notes specialty strips can measure salt.^[7][8]

As one example, Hayward's chemistry quick-start guide for its salt chlorine generators lists a recommended salt level of 2700–3400 ppm, and its AquaRite guide says that model will not make chlorine below 2400 ppm. Your system's manual may differ.^[9][10]

For target ranges and what they mean, see our pool water balance guide.

Test strips, drop kits and digital testers

• Test strips: Taylor describes dipping a strip, waiting a few seconds and matching the pad colors to the chart. It notes strips give a general range rather than an exact number and can be hard to read with color vision deficiency. CDC says strips are less accurate than a DPD kit.^[1][4]
• Liquid drop kits: Taylor explains you collect a sample in a comparator and add drops of reagent. CDC says a DPD kit gives the most accurate chlorine and pH results. Taylor adds that kits take a few minutes longer and need careful reading of directions.^[1][4]
• Digital testers: Latham notes some connect to a smartphone, and that because they vary widely in quality and design, you should follow the device's instructions.^[8]

CDC's rule covers every method: always follow the maker's directions. AquaChek warns never to assume one container's directions apply to another's strips.^[1][11]

Step by step: a good sample and a clear reading

1. Read your kit's directions first, including any waiting times.^[11][12]
2. Use a fresh sample in a clean container. Latham says to rinse each test cell with pool water before using it.^[8][12]
3. Collect water about elbow-deep, away from return jets and chemical feeders, as Taylor advises. PHTA also says to avoid inlets and returns.^[4][12]
4. For drop tests, hold the bottle vertically so drops stay a uniform size.^[13]
5. Read colors in natural daylight with your back to the sun. Taylor says indoor lighting and sunglasses make color matching hard.^[12][13]
6. Take the reading right away unless your instructions say otherwise.^[13]
7. Clean the test cell after each use, then write the results in your pool log.^[2][13]

When results look odd

• Chlorine reads low or zero when you expect it to be high: CDC and Taylor say chlorine above 10 ppm can partially or totally bleach the test, giving a false low reading.^[1][13]
• Alkalinity seems high in a stabilized pool: Taylor notes cyanuric acid above 30 ppm shows up in the alkalinity test. Check your kit's instructions for how to account for it.^[13]
• Mixing brands: Taylor says each maker's reagents have different strengths and color charts are made to match them, so don't swap parts between kits.^[13]

Storing your test kit and strips

• Check the expiration or best-by date on the label, and don't use expired strips.^[11][13]
• Taylor recommends storing reagents and strips at 36°F–85°F (2°C–29°C), out of direct sunlight and away from treatment chemicals.^[13]
• Keep caps tight and keep wet fingers out of strip bottles.^[11][13]
• Taylor recommends replacing reagents and strips each season.^[13]

When to get help

If you find imbalances, AquaChek says to follow the treatment directions that come with your kit or chemicals, or ask your pool and spa dealer. Your written log gives the dealer a helpful record. Latham suggests a monthly water check by a professional.^[11][15]