Quick Definition:

An indicator reagent is used as a way to display the concentration of the presence of a chemical or water quality level in swimming pool water.

What is a Indicator Reagent for swimming pools?

An indicator reagent is a substance used to detect and indicate the presence of various chemicals, substances, and water quality levels in a reservoir of water.

In testing pool water levels such as total alkalinity, calcium hardness, and pH, a process called titration is performed.  During this process, an indicator reagent is used, where the substance is added, and the color of the tested substance changes.  The resulting data and information comes from the end color of the tested substance.

In testing swimming pool water, the pH level is generally identified using a phenol red reagent, which is an indicator reagent.  Other equipment such as a comparator tube, color chart, and other reagents are used during this process.

As mentioned, the ultimate determining factor when using an indicator reagent is the end color of the tested substance.  When specifically using the phenol red indicator reagent, water changes color from red, then to orange when the pH level lowers.  It can also turn yellow, as it goes lower. For this specific type of indicator, the range is 6.8 – 8.0.

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