How to Test Oxygen Levels in Ponds


Oxygen is necessary for the survival of fish and other aquatic species that make their homes in pond settings; however, the oxygen that these animals need is of a different kind from the oxygen that is required by organisms that make their homes on land. The term “dissolved oxygen” (DO) refers to oxygen molecules that have been dissolved in the water and are thus easily accessible to aquatic life for the purpose of respiration. When the concentration of dissolved oxygen (DO) in a pond or another body of water drops to less than 4 to 5 mg per litre, it might be detrimental to the health of the organisms that live in the pond. According to Envii’s research, DO concentrations of less than 2 mg per litre are very dangerous and almost always fatal to fish. Conducting a test to assess the degree of dissolved oxygen (DO) in your pond will help you establish whether or not your aquatic ecosystem provides an appropriate setting for fish and other species.

  1. According to Live Aquaria, the water sample container that comes with the test kit has to be thoroughly submerged until there are no air bubbles left within. It is important to ensure that there is no air leakage by capping the bottle while it is still immersed in the water. Bring the bottle up to the surface, and then use the towel to wipe out any moisture that may be on it so that it will not get slippery as you continue to work with it.

  2. Open the water sample container once more after putting on your protective gloves and glasses, and then put on your safety goggles. First, incorporate the manganous sulphate into the liquid, and then follow it up with the alkaline iodide azide. Both compounds are included in the test kit; however, the box does not specify whether the substances are in powder or liquid form. Add 2 millilitres of each chemical to the test kit if it is a liquid chemical test. In the case of powdered chemical test kits, it is necessary to include the whole quantity of powder that is included in the kit.

  3. Put the cap back on the water bottle, then gently shake it to ensure that the chemicals are properly mixed into the water sample. In the event that DO is present in the sample, the formation of a brown material known as floc will start. Shake the container once again to check if any extra floc will develop after allowing the water to stand for the required amount of time to allow the floc to settle halfway. Allow the water to stand until all of the floc has been absorbed into the water.

  4. The water sample container should be opened, and the sulfamic acid should be added. Use either 2 millilitres of silfamic acid in liquid form or the complete quantity of powder that is included in your test kit. Replace the cap on the container and gently shake it while continuing to combine the acid and the water. The floc will break down, and the colour of the water will change to yellow.

  5. After adding the water and chemical solution to the measuring tube that was included in your kit, you should next transfer the contents of the measuring tube into the mixing bottle. Repeat the process, this time adding one more tube of water to the container that contains the mixture.

  6. While doing so, add the liquid sodium thiosulfate titrant to the mixing bottle while giving the sample in the bottle a gentle stir with one hand. The other hand should be used to add the titrant. Make sure to add the liquid one drop at a time by using a dropper. Count the drips as you add them, stopping briefly in between each one, and stop adding them until the colour of the water changes from yellow to clear.

  7. Divide by 2 the total amount of drops of sodium thiosulfate titrant that you have added. This will provide you with the DO concentration in the water of the pond expressed in milligrammes per litre.

    Things You Will Need

    • Dissolved oxygen kit

    • Water sample bottle

    • Towel

    • Protective gloves

    • Safety glasses

    • Manganous sulfate

    • Alkaline iodide azide

    • Sulfamic acid

    • Measuring tube

    • Mixing bottle

    • Dropper

    • Sodium thiosulfate titrant


    Since the amount of dissolved oxygen in ponds changes on a daily basis due to the amount of sunlight that is available and the temperature of the water, you may want to perform water testing multiple times over the course of a few days in order to get the clearest picture possible of the DO levels in your pond.

    It is possible that different test kits include procedures and quantities of reagents that are somewhat different from those outlined in this article. Always ensure that you are following the instructions that are included with your test kit.


    When working with chemical agents, use extreme care since they are corrosive. Put on protective eye and hand gear, and be sure to wash your hands after you’re done.

    If you are currently treating your pond with chemicals, the test results that you get from test kits may not be accurate.