How to test pool water before you add anything

What to test and the ranges to aim for

Each reading answers a different question. Free chlorine (FC) is what disinfects. pH and alkalinity decide how comfortable the water is and how well chlorine works. Calcium and stabilizer change slowly but set the stage for everything else. These are the ranges Poolora starts with, and where each one comes from:

The ranges are a starting point. If your plaster contractor or equipment manual gives a different number, theirs wins. Write your own targets down once and keep them; they should not change every time you test.

How often to test

The CDC recommends testing chlorine and pH at least twice a day, and more often when many people are using the pool. That sounds like a lot, but chlorine is the reading that moves fastest: sun, swimmers, rain and heat all burn it. pH drifts more slowly, and how fast it drifts depends on your alkalinity.

Alkalinity, calcium and stabilizer move slowly, so most owners check them every week or two, plus after a big rain, a partial refill or any chemical that changes them. Salt only needs a check when the generator asks for it or after adding water.

Take a sample that tells the truth

• Collect water about elbow-deep, away from the return jets and the skimmer. Surface water and water right in front of a jet are not representative.
• Test before adding anything. If you just added a chemical, let the pump circulate it fully before testing again, following the product label.
• Use clean sample tubes and rinse them with pool water first.
• Read results in good light, at the time the kit says. Strips change color if you wait too long.

Strips or a drop kit?

According to the CDC, a DPD drop kit is the most accurate option for home pools and test strips are less accurate. Strips are fine for a quick daily look at chlorine and pH. For decisions that involve a lot of product, such as raising stabilizer, lowering alkalinity with acid or shocking a green pool, use a drop kit.

One trap: chlorine above about 10 ppm can bleach a DPD test and show a falsely low or zero reading. If the water smells and looks chlorinated but the test says zero, dilute the sample with distilled water or use a drop-count chlorine test, and retest. Always follow the kit's instructions and replace reagents when they expire.

Fix things in the right order

Poolora builds every plan in the same order, and it works with any kit:

1. Dilute first if stabilizer or salt is too high. Only replacing water lowers them, and doing it first avoids wasting chemicals.
2. Acid if pH or alkalinity is high.
3. Raise alkalinity (baking soda), then raise pH if it is still low.
4. Calcium, then stabilizer, then salt.
5. Chlorine last. Never add acid and chlorine together.

Add one product at a time with the pump running, let it circulate and retest before the next one. Never mix products in the same bucket.

Put the readings together: water balance (CSI)

pH, alkalinity, calcium and temperature together decide whether water is balanced, aggressive (it dissolves plaster and grout) or scaling (it leaves crusts). The Calcium Saturation Index (CSI) combines them in one number; Poolora treats −0.3 to +0.5 as balanced, the range APSP uses.

Notice that every reading in the second row is inside or at the edge of its own range, yet the water is aggressive. That is why balance is worth checking even when each number looks fine on its own.

Write it down

A test log turns guesses into patterns: how fast your chlorine drops on a sunny week, how much acid a month of tablets costs you, whether stabilizer is climbing. Record the date, every reading and exactly what you added. Poolora keeps this history with charts so you can see trends at a glance.

Keep going

• How much liquid chlorine does a pool need?
• Pool pH and alkalinity
• Pool volume calculator
• Cloudy pool water: causes and fixes