Measuring Dissolved Ozone in Chloronated Water

How to dilute sample to extend test range

Is there a way to measure dissolved ozone (0.5 to 3.0 ppm) in water with a high chlorine level. Yes, there is a way to to this.

First, be sure to use the Indigo Method.

The Indigo Method

“References: Bader H. and J. Hoigné, “Determination of Ozone in Water by the Indigo Method,” Water Research Vol. 15, pp. 449-456, 1981. APHA Standard Methods, 23rd ed., Method 4500-03 B-1997.

With the indigo method, indigo trisulfonate dye immediately reacts with ozone. The color of the blue dye decreases in intensity in proportion to the amount of ozone present in the sample. The test reagent is formulated with malonic acid to prevent interference from up to at least 10 ppm chlorine. Results are expressed as ppm (mg/L) O3.The CHEMetrics Indigo Ozone Vacu-vials® Kit employs an innovative “self-zeroing” feature to eliminate the need to generate a reagent blank. Each Vacu-vials® ampoule is measured before and after being snapped in sample. The change in color intensity, measured in absorbance, between reagent in the unsnapped and snapped ampoule is used to determine the ozone concentration of the sample.”

The indigo test kit can be purchased at the Oxidation Technologies web store. Indigo test kit.

The I-2022 Dissolved Ozone Meter is designed for accurately and quickly measuring ozone in water levels from 0 – 0.75 ppm. This device uses the Indigo Method for testing. This method is based on the colorization of dye by ozone, where the loss of color is directly proportional to the ozone concentration. The results are then displayed on the monitor in ppm (mg/L) of ozone present.

This device has LED display for precise and accurate readout and is easy to use. Once the I-2022 has been purchased the cost per test is only $1.02.

Next, use the dilute method to measure higher concentrations of ozone.


The Indigo snap method test kits will measure up to 0.75 so a dilute procedure can be used to derive an accurate measurement. The video uses the K-7404 kit which used the DPT method, but the principle can be applied to the Indigo kit as well.


Feel free to contact Oxidation Technolgies with any ozone questions.

FAQs about Ozone

Let’s go back to basics. Below is a simple read for the beginner:

  1. What is ozone?
    Ozone is active or supercharged oxygen. It occurs naturally high in earth’s atmosphere and protects us from sun’s cancer causing UV rays. The ozone that we use is generated with eletrical and mechanical equipment. The chemical formula of ozone is O3.
  2. What are some uses of ozone?
    Some common uses are: drinking water purification, wastewater treatment, deodorizing of smells, cooling tower water management, swimming pool water management, effluent treatment and industrial oxidation processes. Ozone Applications
  3. What are some valuable properties of ozone?
    The most important property of ozone is disinfection. Ozone is therefore used for water treatment. Ozone also decolorizes (removal of color) and deodorizes (removal of odour).
  4. How is ozone manufactured and can it be stored like oxygen?Ozone is manufactured from air or oxygen. There is very little or no ozone near earth’s surface. The ozone protective layer is miles above the earth and can not be accessed. Ozone cannot be stored like oxygen. Because of the very high reactivity of ozone, it is very unstable. Ozone decomposes to oxygen rapidly in minutes. Therefore ozone has to be generated at site and used immediately. Ozone Production link

Did You know?

  • Ozone is used in floriculture to decolorize roses to make them white.
  • Ozone gas is pumped into food and vegetable packing to protect them during transportation.
  • Ozone is used to preserve Beer Hops to keep them fresh during storage.
  • Ozone is used for remediation after major fire accidents to remove the smell of fire. This is known as fire restoration.
  • Ozone is extensively used in Hydroponics (growing vegetables without soil).
  • There are nearly 2800 toxic chemicals in cigarette smoke and ozone is effective against more than 80% of those chemicals that have been identified so far.
  1. Has ozone been used to treat drinking water elsewhere?
    Ozone has been used in hundreds of water treatment plants around Europe (France, Germany, UK), USA, and in Asian countries (like China, Singapore). Ozone in drinking water
  2. How long has ozone been known and used?
    Ozone has been known since 1800s and been used in little applications
    before the 80s but more extensively in the 90s. Today ozone use has become very common. History Of Ozone link
  3. Does ozone has any odor?
    Ozone has a slightly sweet smell at very low concentrations but as the
    concentration increases, it becomes irritating. It has a fishy smell. During thunderstorms you get the pleasant smell of ozone. You get the smell of ozone in a Xerox shop and behind television sets.
  4. Will ozone kill bacteria? Or will it stop bacteria multiplication?
    Ozone kills bacteria and is known to be the most effective bactericide on earth. There is no possibility of bacteria developing resistance with ozone.
  5. What about virus?
    Ozone will deactivate virus by attacking the protein of the virus. Virus is a chemical entity and not a living organism. But it has DNAs that replicate fast. Ozone attacks this DNA. Ozone has been proven to act against SARS virus, against AIDS virus and also Swine fl u Virus. But Commercial applications have yet to begin for these applications.