How to Overcome Interference in Pool Water Tests

When chlorine and bromine are in excessive amounts in water, they lead to false pool water test results. In such cases, it is difficult for pool owners to identify the water’s pH and alkaline levels. Thus, drop tests, and color-matching test techniques are vulnerable to discrepancies.

Test results are not only affected by excess levels of sanitizers. Other factors could also lead to inaccurate pool water test results. Nonetheless, the leading cause of incorrect test results is the presence of excessive sanitizing agents. So, let’s find out how to fix these types of inaccuracies.

Color matching 

When the sanitizing agents are more than ten or 15ppm, partial or full bleaching of DPD reagents may occur. As the pool owner, you might conclude that the pool lacks chlorine or bromine, which is not the case. The pool is, in fact, loaded with excessive sanitizing chemicals.

Therefore, if you are sure that chlorine and bromine exist in your pool, and there is no discoloration, dilute the sample and pour in the right concentration. For instance, if you have an affected sample of 10ml, lower it by 5ml, and add 5ml of pure water. Afterward, follow the test guidelines as indicated. Check the resulting color and match it with your chart to identify the pH levels. Every color in the chart is usually paired with a value. Once you determine your test value, multiply it by two to get the accurate reading.

Other interferences:

There are cases where traces of DPD are present in the test cell. This can interfere with the test results, thus ensure you cleanse test cells thoroughly before usage.

Drop test 

Fortunately, drop tests can identify samples with 20ppm of sanitizing agents. But if the sanitizer is more than 20ppm, bleaching occurs and could lead to false readings. Fixing the problem entails diluting the sample with pure pool water and adding an indicator until the example achieves a pink color. Afterward, you should add a titrant until a colorless color appears. Make sure to calculate the titrant drops and double the number to get accurate results.

Other interferences:

A non-chlorine oxidizer known as monopersulfate could interfere with the combined chlorine readings. The quick chemical reaction with DPD will indicate this discrepancy. Usually, it results in an unusually high reading. To solve this problem, use a deox reagent to erase any traces of monopersulfate and perform another test.

Total Alkalinity test (drop-test technique)      

When checking for the pool’s total alkalinity, ensure the pool water turns from green to red for correct results. You will know there is excessive sanitizer if the color of the water goes from blue to yellow. Suppose this is the case, get a new test sample, and add at least five drops of indicator to eradicate any excess halogen. You can then read the correct color and determine total alkalinity.

pH test 

Suppose the sanitizer levels are more than 15ppm; the organic color of the indicator could become affected. You will know this because the sample color will turn purple instead of yellow or red. Once you encounter this problem, pour out the pool water from the test cell, and cleanse it thoroughly. Afterward, get another test sample from the pool and use a dipper to put in one drop of thiosulfate. The chemical thiosulfate makes the pool sanitizing agents in the sample test neutral. Once the sample becomes neutralized, put in the indicator in the test. Then, read your color against the value in the test chart. Be cautious while adding thiosulfate; you will get a false high reading when you add more than a drop of this chemical.

Other interferences: 

Default or old indicators could lead to inaccurate test results. Therefore, upon purchase, ensure your indicator is far from its expiry date. But if you encounter this issue, use a fresh reagent as an alternative.

A chemical known as Poly(hexamethylene) biguanide leads to a peculiar reading when present in the sample. Even so, you don’t need to correct the test sample, the blue to yellow color change is correct. If the sample contains over 30ppm of cyanuric acid, the test results become inaccurate.

Copper/iron test

Copper tests give false readings when large concentrations of iron are in the test sample. Presuming that you encounter this type of problem, dilute the test sample and identify how much concentration of iron is in the sample. Or you can employ a digital reader to identify concentrations of copper and iron.

Calcium hardness test (drop test) 

Calcium hardness tests get affected by metal ions from pipes, water, and algaecides. Some of the most common metals are copper, iron, and manganese. You will identify the presence of these metals in the test sample when there is a purple or red color. If you wish to fix the problem, get a mew sample and put in 5 -6 drops of the titrant. Afterward, add the buffer and indicator and continue with regular pool water testing.

Ultimately, don’t get shocked by false readings. From this article, you can identify what problem your pool is facing as well as fix it.