Critical Components of Pool Water Testing
The way to identify pool problems early is by having your pool properly tested. There are different methods used for testing spa or pool water, and each method has its own pros and cons.
Using dip-and-read test strips is one of the easiest ways to test your pool water. This method will give you a quick check of your water chemistry. Once the pads on the strip change color, they are comparable to standard colors. This will determine whether more testing is needed.
Strips work well to get a view of the overall chemistry of your spa or pool water, but they do have limitations. They are affected by light, your own perception and the color standard limits used for the comparison. In addition, you can run repeated tests and get different results.
Digital Strip Readers
These are one step beyond dip-and-read sticks. The reader will compare the color on your strip to the standard color digitally. This eliminates personal considerations and lighting from the list of factors involved, so it is generally seen as being more accurate than simply using dip-and-read strips.
Free Chlorine Measurement
Beyond the use of test strips, which test all chemistries at once, you have other available options.
Orthotolidine (OTO) uses a drop to test the water chemicals. You can do this test yourself, to test the sanitation level in spas or pools. It is not as accurate as some of the newer methods. This test method does not allow you to get an accurate free chlorine reading, and this makes it difficult to determine how much available chlorine is in the water.
Testing pH Balance
Measuring the pH of your spa or pool is an important part of water testing. Using phenol red is the most common method of testing pH in pool and spa water. The test utilizes a colorimetric drop test which compares the sample color intensity to established color block standards, says
Pool Spa News. It is simple to employ, and is accurate from a 6.8 to an 8.4 on a pH scale. Phenol red can only be used within this range.
To maintain pH properly, you also need to test and then balance your total alkalinity. The most commonly used procedure is titrimetric testing. In this test, halogens are removed, usually through the use of sodium thiosulfate. Then you can test for the total alkalinity. Photometers are also sometimes used for this purpose.
DPD (N, N-diethyl-p-phenylenediamine) Testing
This is useful for the testing of sanitizer, and can test for total and free chlorine. DPD testing may be done like OTO testing. It may also be done by the use of a photometer or titrimetric method. Sometimes results are falsely high with these tests, and human perception, as well as environment and lighting can influence readings.
DPD Titration Testing
This test is also known as FAS-DPD. Rather than comparing colors to standards, it uses a simple balancing reagent. Color indicator is added to each sample, and then a titrating agent will be added until the sample reaches its endpoint, or permanent color change.
This test is more accurate than the DPD drop test, whether your chlorine concentrations are low or high. It measures free chlorine at levels up to 20ppm. This is in contrast to the drop test limit of 5ppm. As with all DPD tests, however, potassium monopersulfate may create false high readings when you are testing for total chlorine.
Interferences with Testing
High chlorine levels and biguanide presence may result in unexpected color changes. This will cause the endpoint to be green or yellow, instead of pink or red. High chlorine levels may be negated by simply adding sodium thiosulfate to your sample before you test it.