Why Is My Dissolved Oxygen Meter Reading Unstable Malaysia
An unstable dissolved oxygen reading does not always mean that the meter is faulty. Movement, temperature changes, bubbles, probe contamination, calibration errors and worn sensing components can all cause the displayed value to fluctuate.
When an Azovtes dissolved oxygen meter produces slow, drifting or inconsistent readings, troubleshoot the sampling conditions and sensor systematically before deciding that the instrument requires repair.
What Does an Unstable DO Reading Look Like?
Common symptoms include:
The reading continuously moves up and down
The displayed value drifts slowly
The result takes unusually long to stabilise
Repeated measurements give different results
The reading changes after the probe is moved
The meter shows an unexpected high or low value
The instrument cannot complete calibration
The reading does not match known water conditions
Small changes may reflect actual variation in the water. Large or continuous fluctuations usually require further investigation.
1. The Reading Has Not Had Time to Stabilise
A dissolved oxygen probe requires time to adjust to the sample.
Stabilisation may take longer when:
The probe moves from air into water
Sample temperature differs from probe temperature
The meter was recently switched on
The water has low circulation
The sensor is dirty
The sensing component is ageing
Keep the probe at the required depth and wait for the displayed result to become steady before recording it.
Do not record the first number that appears on the screen.
2. Water Temperature Is Changing
Dissolved oxygen solubility is affected by temperature. If the probe and sample are at different temperatures, both the oxygen response and temperature compensation may continue changing.
For better consistency:
Place the probe in the sample.
Allow the temperature reading to stabilise.
Avoid holding the sample container with warm hands.
Keep the sample away from direct sunlight.
Record the result only after both readings become stable.
Rapid temperature changes are especially common when moving between indoor and outdoor sampling locations.
3. Air Bubbles Are Attached to the Sensor
Air bubbles on the sensing area can produce an incorrect or unstable result.
Bubbles may form when:
The probe is inserted too quickly
The sensor is tilted incorrectly
Aerated water is being measured
The membrane or sensing surface traps air
The probe is placed directly beside an aerator
Gently reposition the probe to release bubbles. Do not strike the sensor against the container or tank wall.
A bubble attached to the sensor may cause the meter to measure the bubble rather than the surrounding water.
4. The Sample Does Not Have Sufficient Movement
Some membrane-based dissolved oxygen sensors require water movement across the membrane during measurement.
In a stagnant sample, oxygen close to the sensor may be consumed faster than it is replaced, causing the reading to decrease or drift.
Depending on the meter and procedure, users may need to:
Move the probe gently through the water
Stir the sample at a consistent speed
Use a laboratory stirrer
Measure in naturally flowing water
Avoid vigorous movement that introduces new air bubbles into the sample.
Fluorescence-based DO meters are generally less dependent on sample movement, but the probe must still be positioned correctly.
5. The Probe Is Dirty
Wastewater, pond water and industrial samples can leave deposits on the sensor.
Common contaminants include:
Algae
Biofilm
Sludge
Oil
Grease
Minerals
Chemical residue
Fine suspended particles
A coated sensor may respond slowly or produce inconsistent readings.
Clean the probe according to the manufacturer’s instructions. Do not scrape a membrane or optical sensing surface with sharp tools.
6. The Membrane Is Damaged
For membrane-type meters such as the Azovtes JE8803, inspect the membrane for:
Tears
Wrinkles
Punctures
Looseness
Discolouration
Deposits
Trapped air bubbles
Incorrect installation
A damaged or poorly installed membrane should be replaced. After replacement, the sensor may require preparation, polarisation and recalibration before use.
7. The Electrolyte Requires Attention
Electrochemical DO probes commonly use electrolyte. Reading problems may occur when:
Electrolyte is insufficient
Electrolyte is contaminated
The electrolyte has deteriorated
Air bubbles are trapped inside
The wrong electrolyte is used
The probe was assembled incorrectly
Use only the correct consumable specified for the sensor.
Adding more electrolyte without inspecting the membrane and electrode may not solve the problem.
8. The Fluorescence Sensor Cap Is Dirty or Ageing
For fluorescence-based meters such as the Azovtes JE8803A, examine the optical sensing area.
Potential problems include:
Biofilm on the sensor cap
Oil or chemical deposits
Scratched sensing material
Ageing fluorescent coating
Incorrectly installed sensor cap
Moisture or contamination inside the assembly
Clean the sensing surface gently using the recommended method. Replace the sensor cap when it reaches the manufacturer’s replacement condition.
9. Calibration Was Not Performed Correctly
Incorrect calibration can cause the meter to drift or display unrealistic results.
Check whether:
The correct calibration mode was selected
The calibration environment was suitable
The probe was stable during calibration
The sensor was clean
Temperature had stabilised
Required compensation settings were correct
Calibration was completed successfully
If the calibration repeatedly fails, inspect the probe and consumables before attempting it again.
10. Salinity or Atmospheric Pressure Was Ignored
Dissolved oxygen calculations may be affected by salt content and atmospheric pressure.
This is particularly relevant for:
Seawater
Brackish water
Shrimp farms
Coastal monitoring
High-altitude locations
Pressurised systems
If the instrument provides compensation settings, enter the correct values according to the testing procedure.
11. The Sampling Method Is Inconsistent
Two results may differ because the samples were not taken under the same conditions.
Check whether measurements were made at the same:
Location
Depth
Time of day
Distance from the aerator
Water temperature
Flow condition
Weather condition
Probe movement rate
In aquaculture and wastewater tanks, different readings may represent genuine variation across the water body.
Quick Troubleshooting Sequence
When the DO reading is unstable, follow this order:
Allow more stabilisation time.
Check temperature stability.
Remove attached air bubbles.
Confirm the required sample movement.
Clean the sensor.
Inspect the membrane or optical cap.
Check the electrolyte where applicable.
Recalibrate the meter.
Verify salinity and pressure settings.
Test the instrument in a controlled sample.
Compare with another maintained DO meter if available.
This sequence helps separate operating problems from sensor or instrument faults.
When Should the Probe Be Replaced?
Probe servicing or replacement may be necessary when:
Calibration repeatedly fails
Readings remain unstable after cleaning
The membrane is frequently damaged
The electrode is deteriorated
The fluorescence cap has reached its service life
The sensor response remains extremely slow
Results remain unreasonable in controlled conditions
Replacement consumables do not solve the problem
Before replacing the complete instrument, determine whether the issue is limited to the sensing component.
How to Prevent Unstable Readings
Good preventive practices include:
Rinse the probe after every test
Clean it according to the sample condition
Inspect consumables regularly
Store the probe correctly
Calibrate before important measurements
Avoid impact on the sensing area
Keep a maintenance record
Train operators to use the same sampling method
Record measurement time, depth and temperature
Keep replacement consumables available
Consistent maintenance and sampling procedures are the most effective ways to improve dissolved oxygen measurement reliability.
Azovtes Dissolved Oxygen Meter Support Malaysia
MTM Precision supplies Azovtes dissolved oxygen and water-quality meters for aquaculture, wastewater, environmental and industrial applications across Malaysia.
Coverage includes Selangor, Kuala Lumpur, Johor, Penang, Perak, Melaka, Negeri Sembilan, Pahang, Kedah, Perlis, Terengganu, Kelantan, Sabah and Sarawak.
Contact MTM Precision
MTM Precision Sdn Bhd
Website: www.mtmpre.com.my
Email: mtmpre@yahoo.com
WhatsApp: 016-660 7346
Showroom & Service Centre
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia
Contact MTM Precision for help selecting or troubleshooting an Azovtes dissolved oxygen meter in Malaysia.
07 Sep 2026
