Water testing methods

Direct Pool Supplies

What testing method should you use?

You don’t have to be a chemist to keep your pool sparkling clean. To keep things simple, use a testing method that you find fast, easy and convenient. That way you’ll be more likely to stick to your testing regimen. There are two basic types of testing method used by most consumers: test strips and liquid kits.

Liquid kits require that you put a sample of water into a plastic comparator and then carefully add drops of chemical reagent, watching for a change in the colour of the sample. Liquid kits with the reagent OTO were once widely used to measure chlorine, but they have fallen out of favour in recent years. OTO measures only total chlorine, not free chlorine, which is the form of chlorine most effective in sanitizing your pool. In addition, we now know that the chemical reagent in the OTO-type kit can cause cancer.

Kits using the liquid reagent known as DPD do measure free chlorine. However, if you test for free chlorine using a DPD #1 liquid test kit, be aware that high levels of combined chlorine, or chloramines, can cause false-positive results when testing free chlorine. Substances such as monopersulfate (used for shock-treating pools) can also affect the results of the DPD test by causing a false positive reading. Moreover, the DPD test requires careful technique and several steps to get the best results.
Test strips, the easiest method for pool and spa water testing, are fast and simple to use because they eliminate the need to measure samples and count drops. Typically, you simply dip a strip in the water for one second and then remove it. You then compare the colour on the strip to the colour chart on the label.

Industry and water quality experts report that test strips are comparable in accuracy to liquid kits. In fact, many believe they actually deliver greater accuracy than liquid kits because they require less technique. Many local and state health departments now recognize test strips as an approved testing method. This means that professional pool and spa service technicians as well as other industry experts trust the accuracy of pool and spa test strips. Today there are reliable test strips available to test a wide variety of pool conditions, including cyanuric acid and total dissolved solids as well as free chlorine, pH and total alkalinity.

No matter what type of test kit you decide to use, be sure to follow the manufacturer’s recommendations to get the best results.

Q: Why do my Test Strips read 0ppm for free chlorine, while my DPD test shows a free chlorine reading?

A: If there is a high level of combined chlorine in your pool or spa, it is likely the DPD test is showing a false positive for free chlorine and your Test Strips are giving an accurate reading.

Q: Do I need to test as frequently with test strips?

A: Yes. We suggest testing both ends of the pool a minimum of 2 times per week, and spas before each use

Q: Is DPD more accurate?

A: The DPD test for chlorine can be affected by interferences, such as an over-abundance of monochloramines or potassium monopersulfate (used for shock-treating pools). These can give a false positive reading for free chlorine with the DPD chemistry. Recognized technical studies are available to support these claims. In addition, the DPD test requires careful technique and several steps to get the best test

Q: How accurate are test strips?

A: Test strips are at minimum comparable in accuracy to liquid colour comparator tests. Because test strips are more convenient, we believe they actually deliver greater accuracy. They reduce the chances of human error associated with liquid kits, which require measuring samples and counting drops of reagent

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