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Everything You Need to Know About the Bluelab pH Pen

February 09, 2021 6 min read


The Bluelab pH Pen is an icon of the Bluelab fleet and a must-have for serious hydroponic and aquaponic home-growers.

A sturdy, handheld device, the Bluelab pH Pen measures both temperature and pH to make sure your growing solution is providing the perfect conditions for your plants to thrive.

Bluelab pH Pen Features

  • Fully waterproof – not just water resistant
  • Simple two-point calibration process for accuracy
  • One-year peace-of-mind warranty
  • Automatic temperature compensation for accurate readings everywhere
  • Auto-off function to extend battery life
  • 1 AAA battery included - simply power on and go

The pH level of your solution is so important to ensuring your plants have access to the nutrients that are crucial to their development. Equally so, the temperature of your solution can have huge impacts on your plants’ growth rate and structure.

The Bluelab pH Pen takes the guesswork out of growing at home and ensures you get the fundamentals right. The results will speak for themselves.


Designed and built in New Zealand, the Bluelab pH Pen is made by growers for growers. It has a rugged and simple design; featuring a screen for taking readings, three clearly labelled buttons, and a storage cap to ensure the probe doesn’t dry out.

The pen is also waterproof and even floats in case you drop it in your reservoir!


There’s so much to like about the Bluelab pH Pen. Here are a few of our favourite things:

  • Calibration – Bluelab have made this process as simple as possible, with the included manual and care guide extremely easy to follow. The most important thing to note is that the pen must be stored properly to ensure accurate readings – the probe tip must be kept wet at all times to avoid permanent damage.
  • Functions – being able to take readings in both Celsius and Fahrenheit is a big plus, as well as a wide measurement range from 0 to 50 °C and 0 to 14 pH.
  • Hold reading – the hold reading function is seriously convenient, saving you twisting your body into all sorts of awkward angles to take a reading. We don’t know how we ever lived without it!
  • Auto-off – the Bluelab pH Pen will automatically turn off after four minutes of use. You won’t need to worry about unnecessary replacement of batteries if you accidentally leave the pen switched on.


The Bluelab pH Pen is a breeze to operate. You’ll be taking precise pH and temperature readings in no time thanks to its straightforward design.

Here’s how to use the pen:

  • Power on – the pen features a large on/off button – you can’t miss it!
  • Measure pH – remove storage cap, place probe in solution and wait for reading to stabilise.
  • Hold reading – you can “hold” the reading on the screen by short pressing the power button. This helps when you can’t view the readings with the pen in the solution.
  • Change temperature units – the Bluelab pH Pen can be easily switched between Fahrenheit and Celsius depending on your requirements. Just hold down the ‘Units’ button for three seconds until the pen flashes, then short press the ‘Units’ button again to toggle between °F and °C.
  • Rinse and replace storage cap – it’s important that you rinse the probe in clean fresh water after use to ensure accurate pH readings. For maximum lifespan, add three to five drops of KCI storage solution into the wetting seal of the cap each week. Ensure the cap clicks on to prevent the probe drying out – the seal is tight!


Calibration is extremely important to ensure you get accurate readings from the get-go.

You’ll need to calibrate your Bluelab pH Pen before use, as well as a few other situations:

  • If it has been 30 days since last calibration (the check mark/tick will disappear from the LCD screen).
  • If you get an unexpected reading.
  • After cleaning and hydration.
  • After cleaning the batteries.

Here’s how to calibrate your Bluelab pH Pen:

(note: you’ll need pH 7.0 and 4.0 solutions for calibration, or pH 7.0 and 10.0 solutions if your readings are normally higher than 7.0 pH. You can find our Bluelab Calibration Kits here):

  • Clean and rinse – excluding your first use, you must clean and rinse the probe before calibration.
  • Place the probe tip in fresh Bluelab pH 7 Calibration Solution. Always use 7.0 first!
  • Calibrate – long press “cal” button until ‘CAL’ is displayed onscreen. Release the button and a box will flash, indicating calibration has commenced.After the four boxes stop flashing, the screen will show ‘CAL’, indicating calibration is complete.
  • A check mark will now appear at the bottom of the screen to indicate a successful calibration. The mark will disappear after 30 days to indicate calibration is required.
  • Hot Tip: for accurate readings, the Bluelab pH Pen must be calibrated to two points. You should always calibrate to pH 7 first, before calibrating to 4 or 10. This ensures calibration holds and you attain precise readings.


There are a few instances where issues can occur. Luckily, we’ve got the fix for most of these occasions!

  • Readings varying (drift) – drift can occur if your glassware is unclean or if your wick is contaminated or blocked. To clean the wick, just soak the probe in KCI storage solution for 24 hours and retest.
  • Similar readings in all buffers – if your pen is showing similar readings no matter what the buffer value is then your glassware is most likely broken, and you must replace the unit.
  • Unsuccessful calibration – there are a few instances that can cause unsuccessful calibration:
    • Buffers inaccurate – replace buffers.
    • Glassware not clean – clean glassware.
    • Glassware aged (glassware will not clean) – replace unit.
    • Probe not hydrated – soak probe in KCI storage solution for 24 hours and retest. 
  • Readings jumping – this can occur if the contact zone is not sufficiently immersed. Lower the pen into your solution at least 2cm/1” to ensure accurate readings.
  • Displays pH 7 for all buffers – glassware is broken, and the unit needs to be replaced.
  • Incorrect sample reading following successful calibration – this can occur if you have ground loop. You can verify this issue by removing the sample from its environment and measuring in a glass beaker. It may be necessary for the electrical circuitry in your system to be checked.
  • A blocked wick can also cause incorrect sample reading. Simply soak the probe in KCI storage solution for 24 hours and retest.


With the Bluelab pH Pen, it is critical that you take proper care to ensure the pen has a maximum lifespan with accurate readings.

The biggest mistake that people make is letting the tip dry out. You can prevent this by adding three to five drops of KCI storage solution into the wetting seal inside the storage cap once a week.

If you accidentally let the probe dry out, you can rehydrate it in KCI storage solution for 24 hours. Carry out a calibration after hydrating to ensure no long-term damage has occurred.

Here are a few things other things to look out for so that you get the most out of your Bluelab pH pen:   

  • Don’t let the tip dry out – if it dries it dies!
  • Don’t knock the pen – this will break the external glass bulb or internal glass tube.
  • Don’t touch the glass bulb with your fingers – this will contaminate the glass.
  • Don’t plunge a hot probe into a cold liquid (or vice versa) – sudden temperature changes can crack the glass and permanently damage the pen.
  • Don’t immerse in oils, proteins or suspended solids that will leave a coating on the glass bulb.

For more information on getting the most out of your unit, check out the Bluelab pH Pen Care and Use Guide.

Buy the Bluelab pH Pen at The Hippie House today!

Bluelab pH Pen


Bluelab also manufacture a number of other fantastic devices for home growers, such as the Bluelab Guardian Monitor, Bluelab Combo Meter and Bluelab Truncheon Nutrient Meter.

If you have any further questions regarding any of your Bluelab equipment, contact our support team of hydroponic experts to get the most out of your units.

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