How to Read Your Pool Water Test

A pool water test comes back with a lot of numbers, and if you've never been told what they mean, it can feel like someone handed you a lab report. It's simpler than it looks. Each number describes one part of your water, each has a target range, and a few of them affect each other. Once you know the ranges, you can read a test in about a minute. Here's how to take a good sample and what the readings tell you.

Take a good sample first

A test is only as good as the water you bring in. Use a clean bottle and rinse it with the pool water first. Turn it upside down, push your arm elbow deep into the water, and fill it about 12 inches below the surface, well away from the skimmer and the return jets. Surface water can hold sunscreen, pollen and leaves, and water right at a return jet is fresher than the rest of the pool. Neither gives you a true picture.

Cap it, keep it out of the sun and bring it to the counter as soon as you can. Chlorine readings drift as a sample sits in a hot car, so don't let it ride around all afternoon in July.

pH: the number that runs everything else

pH measures how acidic or basic the water is, and the target is 7.2 to 7.8. Think of it as the dial that controls how well everything else works. When pH climbs too high, chlorine loses strength, water turns cloudy and scale can build up on surfaces and equipment. When it drops too low, water becomes harsh on skin and eyes and can wear on plaster, metal fittings and heaters. Small changes matter here, so small adjustments are the rule. Correct pH first, then look at the rest.

Alkalinity and calcium hardness

Total alkalinity targets 80 to 120 ppm. It works like a shock absorber for pH. When alkalinity is in range, pH tends to stay put. When it's low, pH swings around every time you add anything or it rains. When it's high, pH creeps up and refuses to come down. If you have a pool where pH won't hold no matter what you do, alkalinity is the first thing to look at.

Calcium hardness should land between 200 and 400 ppm. Water that has too little calcium goes looking for it and takes it from your plaster, grout and equipment. Water with too much can leave white, crusty scale on tile lines, heaters and the pool walls. Texas tap water varies, so a fill after a big drain or heavy backwash can move this number in a way you didn't expect. It's also one of the readings that changes slowly, which is why it's worth checking in the spring and again before winter.

Cyanuric acid: sunscreen for your chlorine

Cyanuric acid, also called stabilizer or conditioner, targets 30 to 50 ppm. Its job is to shield chlorine from being burned off by sunlight, which matters a lot in a Brazos Valley summer. Too little and your chlorine disappears by afternoon. Too much and the chlorine you do have becomes sluggish, even though the test says you have plenty. The only real way to lower cyanuric acid is to replace some of the water, so add it carefully and test before adding more.

Free chlorine and total chlorine

Chlorine is reported two ways. Free chlorine is the active sanitizer waiting to do its job. Total chlorine is the free chlorine plus chlorine that has already latched onto contaminants. The gap between them is combined chlorine, and it's the thing that gives a pool that strong chemical smell that people mistake for too much chlorine. A pool that smells like chlorine usually needs more free chlorine, not less, or a shock treatment to break the combined chlorine down.

For more complicated situations, a test can also look at metals and bacteria. If your water has a stain or a tint that no chemical seems to fix, mention it when you drop off the sample.

What to do with the results

Change one thing at a time, wait for the water to circulate, then retest. Adding three chemicals at once makes it impossible to tell what worked. Ask for the recommendations in writing or write them down yourself, and ask when you should retest so you know whether the fix held. If you'd rather not haul jugs of chemicals home, ask about chemical delivery. Bring your sample by the showroom on Highway 6 South in College Station, or call (979) 693-8533 with questions.