Chlorine, Bromine & pH Testing in Pool Water
Tablets & Liquids
The testing for disinfectant (chlorine or bromine) and pH in swimming pools and whirlpools must be performed once every two hours while the pool is in operation. The results must be kept in a bound log. The disinfectant and pH tests are also required when a microbial sample is taken (N.J.A.C. 8:26-7.7 & 7.12).
The Phenol Red compound is used for pH testing, and DPD reagents are used for chlorine and bromine.
Both DPD and Phenol Red reagents can be obtained in tablet and liquid form. Your field test kit is designed for use with one form or the other. Do not mix the different forms of testing.
Garden State Labs has tested both tablet and liquid reagents. We have found that when you are using fresh tablets or fresh liquid reagents you will get similarly accurate results. However, our experience has found that liquid reagents tend to age more rapidly than the sealed tablets. This aging begins when the reagent bottle is first opened.
This disparity has caused occasion where significantly different results were obtained. Typically, aged liquid reagents yield a lower disinfectant level than the tablet. For example, an expired DPD liquid will give a 2.5 ppm chlorine result while the DPD tablet will give a 5.0 ppm result.
Garden State Labs periodically checks the accuracy of the tablet reagents which we use for our sampling and analysis. We have found the tablets to be reliably accurate, provided they are not removed from their individual foil packet prior to use.
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Additionally, experience has shown that the use of liquid reagents is more susceptible to human error in the process of testing pH and disinfectant. Liquid reagents require counting individual drops, and depending on the method being performed may also require the mixing of multiple liquids together. This provides the opportunity for miscounting, or improperly mixing the reagents. Tablet reagents are individually packaged for use without counting.
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We strongly recommend that tablets be used for both pH and disinfectant analyses to get consistently accurate results.