Pool Water Testing: Techniques and Restrictions for Pool owners

As a pool owner, the only way to identify if your pool has an issue is to conduct thorough pool water testing. In this article, we will discuss various techniques to implement to test pool and spa water, and their advantages and disadvantages.

Measuring free chlorine

Besides strip tests, there are various techniques you can use to evaluate the condition of pool water.

One approach considered less effective compared to others is the Orthotolidine (OTO) drop test. This technique examines levels of sanitization in pools and spas. However, it does not allow one to identify the chlorine levels in the water.

Another method to measure for sanitization levels in the water is the DPD (N, N-diethyl-p-phenylenediamine) test. It also offers a free chlorine test, enabling pool owners to know the water’s exact levels of chlorine. Similar to OTO, it uses a control color to identify the condition of the water. You can do this technique using a titrimetric test or, at times, a photometer. It is the most popular and affordable technique.

However, when there are concentrated chlorine levels, say 10-15 ppm, that may lead to inaccurate results since bleaching of the color may occur. Moreover, levels of chlorine are significantly lowered at high pH readings. It is important to note that 0.5 ppm levels of combined chlorine can disrupt the normal functioning of DPD and lead to incorrect results. In such a case, the free chlorine test will read a false high. Thus, the user will not be able to pinpoint combined chlorine in the water. Therefore, this technique has a disadvantage because test results get affected by individual perception, lighting, and surroundings.

FAS-DPD, also known as DPD titration testing, uses a slightly different testing procedure than the typical DPD testing. Instead of using colors to identify test results, it utilizes a testing agent. First, color is put into the specimen before adding a titrating agent. Afterward, the user waits until they see a change of color. The quantity of sanitizer in the pool will be identified by the percentage of titrating agent required for a color change. This method is more effective than the DPD technique at any concentration of chlorine levels. Unlike the DPD technique, FAS-DPD can estimate levels of chlorine for free until 20ppm is attained. Both methods are prone to false high results during chlorine pool water testing because of the existence of potassium monopersulfate.

Strip tests

Strip tests are one of the most straightforward techniques you can use for pool water testing. They work efficiently for checking water chemistry in a pool or spa. How do they work? Strip test pads contain substances bound to react with elements in the water. After a few minutes of reaction, the color of the test pads changes and can determine the water condition. The advantage of strips is that one gets to know the state of the entire pool.

Nonetheless, several disadvantages come with this technique. The state of lighting in the pool significantly impact on the proper functioning of test strips. There’s also a limitation on the colors for differentiation on the strip. Consequently, you will not get consistent test results at times.

A more advanced form of the strip test is the digital strip reader. It differentiates the specimen color from the custom color. It also compares the color to a concentration using a sequence of mathematical calculations. A Digital dip-and-read strip is more accurate than the regular strip test. The reason being, individual notions and lighting do not affect this strip. But in general, the digital strip test also has cons that might interfere with the validity of the test results.

pH balance

Calculating pH levels is crucial in facilitating the right water conditions in a pool. Most pool and spa owners test for water pH using a substance known as phenol red. Like OTO, this is a colorimetric drop test that differentiates the sample color from the standard color. It is a relatively simple and appropriate way to test for pH levels. However, on the pH scale, it is only correct from 6.8 to 8.4; phenol is not a reliable method outside this range. When the water contains high levels of bromine and chlorine and reacts with phenol red, it turns to a dark purple color indicating a pH of at least 6.6.

Contrary to what you might be thinking, this pH is relatively low. Solving this problem would require one to implement a neutralizing agent. Alternatively, you can also use pH meters to check for pH levels. Unlike phenol red, it is not limited to a specific range. However, you should carefully adjust it to facilitate correct results.

Pool owners should also ensure correct pH levels. Therefore, they must test for alkalinity. The most common method to do this is through Titrimetric testing. The total quantity of titrant used eventually gives rise to an alkaline reading. Before using this technique to test for pH, eliminate halogens, and incorporate photometers.

Popular disruptions

During pool water testing processes, you are likely to encounter some disruptions. Excess concentration of chlorine and the existence of biguanide lead to an abnormal change of color. Test results often result in yellow or green color when there’s any form of disruption compared to the typical pink color. However, you can use sodium thiosulfate to decrease chlorine levels.