- No bacteria to deplete the oxygen.
- No food to deplete, there is no BOD in the sample.
- The dissolved oxygen measuring device is not functioning so it is always reading the same value.
- Certain samples are not suitable for BOD analysis. If there are large amounts of toxic metals in the sample, COD is the only way to be certain of the oxygen demand of the sample.
- Check the sample for chlorine. Any residual chlorine will cause no depletion regardless of seeding.
- Neutralize any chlorine in the sample, set the pH to 6.5-8.5, then seed the sample. If the sample has ever been disinfected, you must seed the sample.
- GGA must be seeded. If you are attempting to run GGA unseeded, it really should not deplete anything at all.
- Verify that the dissolved oxygen measuring device is actually measuring lower dissolved oxygen values by checking what happens when the probe is placed in a 300 mL BOD bottle filled with water that has had 300 mg of sodium sulfite added to it and a single grain of cobalt chloride.
- If the dissolved oxygen measuring device still measures above 1 mg/L it is broken, replace the device with another unit.
- If the dissolved oxygen measuring device measures something less than 0.1 mg/L then it is functioning correctly.
- If the dissolved oxygen measuring device measures something between 0.1 mg/L and 1 mg/L, it is necessary to reset the zero value for the unit. Follow the manufacturer's instructions on how to do this.