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Water-testing techniques do matter

By Marcelle Dibrell

Testing remains the single most important tool in a service professional’s arsenal for ensuring both the safety and balance of the water. 

In fact, for a pool and spa service professional, water chemistry testing is the only way to know that you have achieved water balance and sanitation. It is not enough to visually confirm that the water looks clear, and is therefore in good shape. Clear water is not an indicator that bacteria or algae is not present, and it says nothing about whether the water could be damaging to the pool’s surface, plumbing and equipment. 

But testing is only useful if the tester is observing the proper testing techniques. That is the only way to ensure any level of accuracy or precision. It is essential to follow a simple standard operating procedure for sample collecting and testing. 

Clearly, this begins with proper sampling techniques. The first step is to get a fresh water sample in a clean container. Sample holders that contain residual water from a different pool or contaminants from a previous test will not provide any information about the water that is currently being tested. 

Next, work with a sample that is representative of the conditions of the pool as a whole. It’s like taking a poll – we want answers that reflect the general state of affairs, not the anomalies. 

Therefore, be sure to rinse the sample container with the water and get a sample from deeper than 18 inches below the water surface. We do this because the water at the surface is not representative of the water chemistry of the pool as a whole. This is where the debris and the oils float. It is also where the water is interacting with air, and it’s where evaporation is taking place.

Avoid sampling near water inlets and returns. This water is also atypical of the pool as a whole. It is water that has just returned from the filter, or water that was just exposed to chemical treatment. We do not need information about water that has different chemical concentrations than the main body of the pool. 

And while it may be obvious, it must be said: never test the water immediately after chemical addition. Clearly, this water has not achieved the degree of mixing necessary to provide information about the state of the total water volume. 

It’s a good idea to take water from the approximate middle of the pool, rather than from corners or steps, which may not have achieved the degree of mixing that the majority of the water has. Some experts even recommend testing from both the shallow and deep ends, and then averaging the results to truly get a representative idea of the condition of the pool water. 

The treatment of the testing equipment is just as important. 

Start the season with fresh reagents. These reagents are perishables; they lose potency through chemical reactions of their own over time. This happens even in ideal conditions, but the reagents can be made to deteriorate more quickly when conditions are not ideal. For that reason, store the test kit and reagents in a cool, dry place, out of direct sunlight and away from pool chemicals. Extremes in temperature, as well as exposure to air, sunlight, moisture, and other chemicals will diminish their potency or usefulness. If there is any doubt about the integrity of your reagents, test your test kit using standards, or simply replace your reagents with fresh ones. Standard protocols include:

•Keep the reagent bottles, containers, vials, test tubes, comparators, dip-cells and hands clean and dry.

•Avoid cross contamination between reagents. Keep reagent bottles tightly capped and never interchange caps.

•After testing, clean and rinse equipment completely to avoid staining or cross contamination and allow it to air dry.

•Do not use contaminated, old or expired reagents.

Do not interchange reagents or products between manufacturer’s test kits. While manufacturers may use some of the same reagents for each type of test, these reagents may be in different concentrations from source to source. And since so many tests rely on color changes, those varying concentrations result in different shade variations. Similarly, the view depth of the test cells also varies from one manufacturer to another, which also results in color variations, so do not swap out test cells from one kit to another. 

Finally, accurate results depend on your testing method. 

Read and follow all instructions thoroughly. Manufacturers tests are different from one another – the procedures are not one-size-fits-all. Also, occasionally one manufacturer may change their testing protocol from one year to the next. 

It is also essential to get the proper exposure of a reagent to the pool water chemistry. 

For example, a test strip manufacturer may instruct the operator to dip for 2 seconds or 5 seconds. That time frame matters because the color development depends upon exposure time. Similarly, wait times between reading test results may vary from one test kit to another; if the wait time is not followed, the results will be unreliable. 

On a related note, mix the sample as directed. If the directions say to swirl the vial, but you shake the sample instead, you may change the pH. 

For tablet-based tests, crush the tablet as directed and allow it to completely dissolve or the reaction will not be complete. Use the caps that come with the cells for inversion mixing. 

Do not use your fingers, which contain oils and other contaminants that may interfere with the results. 

It is equally important to work with the proper volume of water and to add the appropriate amount of reagent. Just like a recipe, the quantity of each ingredient has been especially formulated to provide the desired result. Measure the volume of the sample carefully. Add water to the meniscus.

When adding drops of a reagent, it is best to hold the bottle vertically to get even sized drops. Follow “endpoint + 1 drop” rule. But do not count extra drop if color is unchanged. 

Avoid testing at the very top or the very bottom of a test kit’s range. These portions of the range often have poor accuracy.

For color matching tests, conduct the test in natural daylight. These tests are generally designed to be read in daylight. A different, artificial light source will affect your perception of color and therefore alter your test results. Use indirect light with your back to the sun. On a related note, use a white or neutral color for a background for colorimetric testing. 

On a final note, practice good housekeeping. Do not dispose of solutions in the pool or spa, and follow local, state, or federal guidelines. Keep chemicals away from kids. Do not use glass sample containers that could shatter and hurt someone. Wipe up spills promptly. While it may not affect the test, it is just good manners.

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