How to Measure Dissolved Oxygen in a Fish Pond Correctly Malaysia

Measuring dissolved oxygen in a fish pond involves more than placing a probe into the water and recording the first number displayed. Time, depth, location, water movement, temperature and probe condition can all affect the result.

Using an Azovtes portable dissolved oxygen meter with a consistent testing procedure helps Malaysian aquaculture operators obtain readings that are easier to compare and use for pond-management decisions.

Why Measure Dissolved Oxygen in Fish Ponds?

Fish and shrimp absorb oxygen from the surrounding water. When dissolved oxygen becomes too low, aquatic animals may experience stress even if the water still appears normal.

Low oxygen conditions may contribute to:

Reduced feeding
Slower growth
Fish gathering near aerators
Fish gasping at the surface
Increased disease susceptibility
Poor feed utilisation
Sudden mortality in severe cases

Dissolved oxygen can change significantly within the same day, so one occasional reading may not represent the actual pond condition.

What Affects Pond Dissolved Oxygen?

Important factors include:

Water temperature
Sunlight
Algae and aquatic plants
Fish and shrimp respiration
Stocking density
Feeding rate
Decomposing organic matter
Rainfall
Cloud cover
Aerator operation
Water depth
Water circulation
Incoming-water quality

Understanding these factors helps operators interpret why readings change.

What Is the Best Time to Measure?

Early Morning

Dissolved oxygen often reaches its lowest level around the period before sunrise.

During the night:

Photosynthesis stops
Fish continue consuming oxygen
Plants and algae consume oxygen
Microorganisms decompose organic matter
Oxygen may continue declining until daylight returns

Early-morning measurement is important because it helps reveal the pond’s low-oxygen condition.

Afternoon

During daylight, algae and aquatic plants may release oxygen through photosynthesis. Afternoon readings can therefore be considerably higher.

Comparing morning and afternoon measurements helps operators understand the daily oxygen fluctuation.

During High-Risk Conditions

Additional measurements may be needed:

After heavy rain
During several cloudy days
During very hot weather
After heavy feeding
When an aerator fails
After chemical treatment
When fish behave abnormally
During algae die-off
After introducing new stock
Before increasing stocking density

Where Should the Pond Be Tested?

One location does not always represent the complete pond.

Useful measurement points include:

Near the water inlet
Near the outlet
Close to an aerator
Away from the aerator
Near feeding areas
At the pond centre
In corners with weak circulation
Areas where organic waste accumulates

A good reading beside an aerator does not confirm that the entire pond has sufficient oxygen.

Use the same monitoring points each day so results can be compared properly.

At What Depth Should DO Be Measured?

Dissolved oxygen may differ between the water surface and deeper areas.

Surface water may have more contact with air and sunlight. Deeper water may have:

Less mixing
Lower oxygen
More decomposing material
Greater contact with bottom sediment
Different temperature

For shallow ponds, a consistent mid-water measurement may be useful for routine checks. For deeper ponds, measurements at several depths can reveal oxygen stratification.

Always record the measurement depth.

Do Not Place the Probe in Pond Mud

If the probe touches the pond bottom, it may disturb sediment and expose the sensor to water with very different local conditions.

This can:

Contaminate the sensor
Produce an unrepresentative reading
Release organic material
Damage the membrane or sensing cap
Increase cleaning requirements

Keep the probe suspended at the selected depth.

Prepare the Dissolved Oxygen Meter

Before entering the field:

Inspect the probe and cable.
Confirm the battery condition.
Check the membrane or fluorescence cap.
Clean the sensor if necessary.
Calibrate the meter according to its instructions.
Confirm relevant compensation settings.
Prepare a field-record sheet.
Bring clean rinse water.
Carry required spare consumables.
Protect the instrument during transport.

A damaged or poorly maintained probe cannot be corrected by careful sampling alone.

Correct Fish-Pond DO Measurement Procedure

Step 1: Select a Monitoring Point

Use a predetermined location. Record its name or reference number.

Step 2: Lower the Probe Carefully

Lower the probe to the required depth without allowing it to strike the pond wall, aerator or bottom.

Step 3: Remove Attached Bubbles

Inspect or reposition the probe gently to release bubbles from the sensing surface.

Air bubbles may cause misleading readings.

Step 4: Provide the Required Water Movement

Some membrane-based sensors require water movement across the sensing membrane.

Depending on the meter:

Move the probe gently
Use the natural water flow
Follow the specified stirring method

Avoid vigorous movement that introduces new bubbles.

Fluorescence-based meters are generally less dependent on sample movement, but correct positioning is still necessary.

Step 5: Allow the Reading to Stabilise

Do not record the first displayed value.

Wait until:

The DO result becomes stable
The temperature stabilises
Large fluctuations stop

Step 6: Record the Complete Conditions

Record:

DO result
Temperature
Date and time
Pond number
Location
Depth
Weather
Aerator status
Fish behaviour
Recent feeding or treatment

Step 7: Repeat at Other Points

Move to the next monitoring point and repeat the same procedure.

Step 8: Rinse the Probe

Rinse the sensor between ponds to reduce contamination and disease-transfer risk.

Measuring Near an Aerator

Testing beside an operating aerator can help verify local oxygenation, but it may not represent the rest of the pond.

Compare:

Near the aerator
Midway across the pond
Furthest area from the aerator
Areas with weak circulation

Large differences may indicate uneven oxygen distribution or inadequate water movement.

Should the Aerator Be Switched Off During Testing?

This depends on the measurement objective.

Keep it operating when checking the oxygen condition under normal farm operation.

A controlled comparison before and after aeration may help evaluate system performance, but operators should not switch off critical aeration if doing so could endanger fish or shrimp.

Aquatic-animal safety takes priority over conducting a test.

Membrane vs Fluorescence DO Meter for Pond Testing

Membrane DO Meter

A membrane-type meter may be suitable for routine aquaculture use when staff can manage:

Membrane replacement
Electrolyte
Probe preparation
Required sample movement
Regular calibration

Fluorescence DO Meter

A fluorescence meter may be practical for users who:

Measure many ponds daily
Prefer reduced membrane-related maintenance
Need convenient spot checks
Test water with limited natural movement

Both technologies require cleaning, calibration or verification, and correct storage.

Common Fish-Pond Measurement Mistakes

Avoid:

Measuring only in the afternoon
Testing only beside an aerator
Using inconsistent depths
Letting the probe touch sediment
Recording before stabilisation
Ignoring water temperature
Using a dirty sensor
Failing to calibrate
Moving the probe too aggressively
Comparing readings taken under different conditions
Testing only after fish show visible distress

Why Do Readings Differ Across the Pond?

Variations may be caused by:

Uneven aeration
Different water depths
Algae distribution
Localised organic waste
Feeding activity
Poor circulation
Temperature differences
Distance from the inlet
Bottom conditions
Measurement technique

Repeat unusual measurements before assuming the instrument is faulty.

Creating a Daily Pond DO Record

A practical record can include:

Information	What to Record
Pond	Pond number or name
Time	Exact measurement time
Location	Inlet, centre, outlet or aerator area
Depth	Measurement depth
DO	Dissolved oxygen result
Temperature	Water temperature
Weather	Sunny, cloudy or raining
Aeration	On, off or operating hours
Feeding	Time and quantity
Observation	Fish behaviour, algae or water colour
Action	Aeration, water exchange or follow-up

Trend records are more valuable than isolated readings because they show how the pond changes over time.

What Should You Do After an Unusual Reading?

When the result is unexpectedly low or high:

Allow the sensor to stabilise again.
Check for air bubbles.
Inspect the probe.
Repeat the test at the same point.
Measure at another location.
Confirm temperature.
Check calibration.
Compare with fish behaviour and aerator condition.
Follow the farm’s approved response procedure.
Seek professional aquaculture advice where necessary.

Do not make a major pond-treatment decision from one unverified result.

Choosing an Azovtes DO Meter for Fish Ponds

Before purchasing, provide:

Fish or shrimp species
Number and size of ponds
Pond depth
Expected DO range
Daily testing frequency
Required cable length
Preferred sensing method
Operator maintenance capability
Need for morning and field measurements
Availability of replacement consumables

The best meter is one that farm staff can use consistently and maintain correctly.

Azovtes Fish-Pond DO Meter Supplier Malaysia

MTM Precision supplies portable dissolved oxygen and water-quality meters for fish farms, shrimp farms, hatcheries, aquaculture research and pond-management services 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 assistance selecting an Azovtes dissolved oxygen meter for fish-pond monitoring in Malaysia.