How to Test Oxygen Levels in Ponds


Oxygen depletion occurs when the need for oxygen by the fish in your pond exceeds the oxygen available. According to the University of Georgia, once fish begin to die off, it is usually too late to correct the imbalance. If your fish stop eating or are found at the surface late at night or early in the morning, your pond may be low in oxygen. By using simple techniques and an oxygen detecting kit, you can foresee an episode of oxygen depletion before it happens.

Things You'll Need

  • Barometer
  • Titration tube
  • Direct reading titrator
  • Manganous sulfate solution
  • Alkaline potassium iodide azide
  • 1:1 sulfuric acid solution
  • Starch indicator solution
  • 0.025N sodium thiosulfate solution
  • Water sampling bottle
  • Protective gloves
  • Safety goggles

Testing Procedure

  • Read the barometric pressure from the barometer. Remove the cap of the water sampling bottle and immerse it in the water for two to three minutes. Be sure there are no air bubbles in the sample. Remove the sample.

  • Wearing protective gloves and goggles, add eight drops manganous sulfate solution and eight drops alkaline potassium iodide azide solution. Cap, and repeatedly invert the bottle to mix the solution. If oxygen is present, a brown-orange precipitate called floc will form.

  • Let the bottle stand until the top half of the sample is clear. Invert repeatedly again to re-mix. Let stand until the top half is once again clear.

  • Add eight drops of 1:1 sulfuric acid solution. Mix as in previous steps. A clear yellow to brown-orange color should develop. The sample is now fixed. If you need to take samples from multiple ponds, repeat steps 1 through 4 before moving on to step 5.

  • Fill the titration tube with 20 ml of sample. Cap the tube. Fill the titrator with 0.025N sodium thiosulfate. Insert the titrator into the titration tube through the center hole in the cap. Swirl the tube gently while pressing the plunger. When the yellow brown solution becomes a fainter yellow color, stop. If the solution was already faint yellow, skip to the next step.

  • Remove the titrator and cap from the tube. Carefully add eight drops starch indicator. The solution should turn blue. Replace the cap and titrator. Slide the titrator into the tube until the solution turns clear. Read the result from the scale on the side of the tube at the plunger tip.

Tips & Warnings

  • If the plunger reaches the end of the tube before the color turns clear, repeat the procedure with a fresh sample and add the original result to the final result.
  • Wear gloves and goggles for this procedure. If you get the solution on your skin, wash immediately.

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