Swimming Pool Chemical Testing: Methods and Techniques

Swimming pool chemical testing | Clear Comfort AOP Pool

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Checking pool and spa chemical levels is an important practice that pool owners and operators often overlook. Swimming pool chemical testing is critical because it validates water quality and determines the necessary dosages for correcting water chemistry issues.

If your water chemistry is out of balance, you can end up with corrosive or scale-forming conditions that can be very costly to correct if left unchecked for too long. In addition, accurate chemical testing is critical for the calibration of automatic pool chemical control systems.

Pool Chemical Testing Best Practices

Store Your Chemical Reagents

When using any test method that uses chemical reagents it is important to store and handle them correctly. Improper chemical storage and handling can lead to injury, so make sure you are taking the right precautionary steps.

  • Store chemical reagents in a cool, dry place, out of direct sunlight and within the specified temperature range
  • Do not allow reagents to freeze
  • Rotate reagent stock to use the oldest first, discarding expired reagents
  • Replace and tighten caps on any liquid reagents
  • Always rinse the sample collection and testing containers with fresh water after each use

Take Deep Water Samples

Regardless of the method you choose, collect the water sample you are analyzing from a depth of about 18 inches below the surface and away from any return inlets. The reason for this is to ensure that the sample is representative of the water as a whole. Water from return inlets may have higher concentrations of chemicals and the highest concentration of contaminants is at the surface.

Water Quality Testing Methods

There is a variety of swimming pool chemical test methods available on the market today, each with their own pros and cons. Here are some of the most common:

1. Dip-and-Read Test Strips

Dip strips are convenient for residential pool and spa use due to their ease of use and affordability. Chemically-treated reagent pads are affixed to the plastic strips which are dipped into the water sample. After the specified time has passed, the pads change colors and you must compare them to the standards printed on the container.

Dip-and-read strips are typically not as accurate as some other methods and are not recommended for commercial facilities. 

2. Colorimetric and Titration Test Kits

Some of the most common test methods employ the use of liquid and/or powder reagents. Colorimetric testing adds a reagent to a sample, which results in a color change that you compare to the comparators on the test vials.

There is a level of subjectivity to this type of testing where different people may perceive different colors.  Some comparators measure in increments of 1 ppm (parts-per-million) or more, which leads to some guesswork and reduced accuracy.

Titration methods remove some of those issues by adding reagents dropwise until a drastic color change endpoint is reached.  Hold liquid reagent dropper bottles straight up and down to achieve a consistent and correct drop size. Always use comparator covers to mix, rather than your hand, as chemicals and contaminants on your skin can alter results.

3. Photometric Tests

Photometers beam a specific wavelength of light through a sample treated with reagent and compare the amount of absorption to that of a blank sample. Some photometer tests require a wait time for the chemical reaction of the reagent and sample to complete.

If performed correctly, photometric testing can yield some of the most accurate and reliable results.  

4. Electronic Tests

Electronic testing is used continuously in most automated chemical controllers and is also available in handheld meters. If you choose this method, be sure to know that electronic meters require frequent calibration and cleaning of the probes to maintain accurate readouts.


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