How often should I test my pool water?

The short schedule

Test free chlorine and pH on every day the pool is in use, or at least every few days when it is quiet, and test total alkalinity, calcium hardness and stabilizer once a week. That is a home version of what the Portsmouth Health Department's operator guide sets for public pools. It says that chlorine and pH levels should be checked every day before the pool is opened, and after that every two hours,^[1] and that total alkalinity, calcium hardness and stabilizer (cyanuric acid) must be checked weekly.^[1]

Portsmouth's code requires free chlorine and pH tests to be made and recorded at least once every two hours while a pool is in operation, and alkalinity and calcium hardness tests at least weekly.^[1] A backyard pool does not need two-hour checks, but the numbers show what matters: chlorine and pH change fast, the other readings change slowly. The guide also makes the broader point that pool water testing is one of the most important maintenance tasks involved in operating a pool.^[1]

What to test, and the target

Virginia's water quality standard for pools keeps free chlorine between 1.0 and 3.0 ppm and pH between 7.2 and 7.8.^[2] That standard governs regulated pools, but it is a sensible target for a home pool too. The slower readings have targets in the Portsmouth guide: the acceptable range for total alkalinity is 80 to 120 ppm,^[1] and the recommended cyanuric acid level is 40 to 60 ppm, and it should be checked weekly once the proper level is reached.^[1]

If a reading is out of range, how to balance pool chemicals walks through what to add and in what order.

When to test more often

The guide's rule is that the more often pool water is tested, the more quickly, safely and easily improper levels can be corrected.^[1] Add extra checks when:

• It is hot and sunny, since heat and sun use up chlorine quickly.
• There has been a storm or heavy rain.
• The pool has had a crowd, or a lot of children.
• The water looks even slightly hazy or green. Why a pool turns green explains what to do when it already has.
• You have just added a chemical, which calls for a retest before adding another.

Testing also decides how much chemical you buy; see what pool chemicals cost per season in Virginia.

Testing well

A frequent test is only useful if it is accurate. Take water samples from 12 to 18 inches below the surface, and not from corners or directly in front of return lines.^[1] Corners are dead spots, and return lines give water that has just left the filter and chlorinator, which reads high.

Pool test kits are not 100% accurate, so use fresh reagents and replace them at the start of each season.^[1] Sun and heat can drastically age and weaken reagents, so keep them in a cool, dry, dark place.^[1] Rinse the tubes before and after each use, and cap them instead of covering them with your fingers.

Know the kit's limits. Some chemicals in the pool water, such as cyanuric acid, may cause problems with the accuracy of the alkalinity test.^[1] Taking a sample to the store that sells you chemicals is a free cross-check in many shops, and a good idea at the start of the season.

Keep a log. Date, readings, weather and what you added take a minute and show a drift before it turns into a problem.

Stop and call a pro if

• Readings will not stay in range after you correct them and retest. That can point to a filtration, circulation or stabilizer problem.
• The water goes cloudy or green even though your tests look fine. Compare with a store test and see why pool water turns cloudy.
• You cannot test regularly. Whether a pool service is worth it depends on how much of the routine you want to hand off.
• The repair would cost $1,000 or more. If the work you are considering is valued at $1,000 or more, a valid Virginia contractor's license is required.^[3]

Getting help in Virginia

Browse pool and spa services or more pool and spa answers.

When you want a pro to take over the routine, describe your pool and local pool companies quote it.