FAQ and troubleshooting: Bluelab Combo Meter

General Questions:

Bluelab Combo Meter 1-small (1)

How do I change the nutrient and temperature units?

  1. Press and hold the ‘nutrient/units’ or ‘temp/units’ button until the display starts flashing. Release, then short button press the same button to scroll through the units.
  2. Release when the required unit is displayed.
  3. The display flashes four times after the last button press then returns to a normal display, showing the selected unit.

How do I change the batteries?

  • Batteries are replaced in the Bluelab Combo Meter when the low battery indicator appears on the screen.
  • Open battery compartment by sliding the back cover down and insert 2x AAA batteries as shown on the battery holder. Slide the cover back on. Note: Alkaline batteries are recommended.
  • Important: Check the batteries at least every 6 months for signs of deterioration, rusting or swelling.

How often do I have to clean and calibrate my probes?

When the calibration indicator disappears from the display (every 30 days) remember to:

  1. Clean the pH probe tip with Bluelab pH probe cleaner.

  2. Hydrate / store the sensor. Ensure the cap always contains KCl Storage Solution.

  3. Clean the conductivity probe tip.

    The Bluelab Probe Care Kit pH and Conductivity can help you with all your cleaning and calibration needs.

There is a salt crust on my pH probe – why?

  • The pH probe and the storage cap contains KCl (Potassium Chloride) solution. The result of a small level of evaporation of KCl is the formation of a salt crust as KCl is a type of salt.
  • This salt crust is normal and will not harm the probe or meter. Gently wash the salt off under fresh running water. It is essential to ensure that your probe always has sufficient KCl in the storage cap to remain hydrated.

My pH probe has accidentally dried out, what should I do?

The probe must be rehydrated for 24 hours in KCI storage solution (never use RO, distilled or deionised water). Next, carry out a calibration to check the probe hasn’t suffered permanent damage.

My pH reading is stuck on 7 pH, what should I do?

Inspect the glassware for damage. If your meter pH reading is stuck on 7 pH (or close to that), it is likely the glassware is damaged. The pH probe likely needs replacing.

How do I replace the pH probe?

1. Attach the probe: Connect the probe to the meter via the BNC fitting.

2. Loosen the storage cap. Hold cap and twist base one full turn, then gently remove. Not loosening before removal will damage the probe.

3. Calibrate your probe to your Combo Meter. Read how to calibrate your probe here.
After calibration, it is now ready to use. Caution: always keep your pH Probe stored hydrated with Bluelab KCl Storage Solution.





Nutrient reading low

Contaminated conductivity/ temperature probe

Clean conductivity/ temperature probe

Solution temperature low/ high

Wait 5 to 10 minutes for reading to stabilise to a constant value

Temperature reading inaccurate

Contaminated pH probe

Clean pH probe

Incorrect calibration

Ensure calibration solutions are accurate. Replace if in doubt. Wait longer for readings to stabilise before calibrating to a constant value

Calibration unreliable

Calibrate pH probe

pH probe damaged or old

Replace pH probe

pH reading does not change from solution to solution

Broken glass bulb, tube or connector

Check pH probe for damage. Replace pH probe

Displays low battery indicator *Battery image*

Insufficient power to take a reliable reading

Replace the batteries. DO NOT use rechargeable batteries

No display

Batteries dead or inserted incorrectly

Check batteries are inserted correctly. Replace if necessary

Display shows ‘Err’

Problem with pH calibration

See error message descriptions in section 10 of the Bluelab Combo Meter Manual

While in pH mode

Over range pH.
Under range pH

Solution > 14.0 pH.
Solution < 0.0 pH.
Check pH probe connection. pH probe could be faulty. Combo Meter could be wet inside

While in temp mode

Over range temperature. Under range temperature

Solution >51 °C / 122 °F.

Solution <0 °C / 32 °F.

Conductivity/temperature probe or Combo Meter faulty.

While in conductivity/ nutrient mode

Over range conductivity/ nutrient

Over range conductivity >9.9 EC, 99 CF, 4950 ppm 500, 6930 ppm 700. Conductivity/temperature probe or Combo Meter faulty.

Further resources:      

Getting started: Bluelab Combo Meter

How to hydrate your pH probe

How to clean Bluelab pH Pen and Bluelab pH Probes [+ video]

FAQ and troubleshooting for Bluelab pH probes