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How to Calibrate Bluelab pH Pen – 8 Helpful Step-by-Step Instructions

A pH meter or pH pen is a scientific tool to check the number of hydrogen ions in various mediums to calculate their pH levels. Bluelab pH pen is one of the most widely used pH meters by gardeners to test the acidity or alkalinity of the soil or water.

Before checking your pH levels, you need to calibrate your pen to get accurate readings. Follow our simple and helpful instructions to learn how to calibrate Bluelab pH pen.

All plants have nutritional requirements to be met to achieve healthy growth. If the pH of your soil is not right, the plants might not be able to obtain certain nutrients, which may retard their growth.

That is why you need to check the pH of your growing medium regularly and maintain it to an optimal level. Follow the instructions to learn how to calibrate the Bluelab pH pen and use it.

How to Calibrate Bluelab pH Pen
Bluelab PENPH pH Pen – via

How to Calibrate Bluelab pH Pen?

Being a gardener, you know how important it is to maintain the pH level of your growing medium to ensure healthy growth and a good harvest of vegetables. To maintain the optimal pH level, you need to check it every once in a while, and for that, you need a pH pen. You can buy a Bluelab pH pen here.

bluelab pH Pen-Digital pH Tester - Reliable & Accurate for High Yield Crops - Hand-Held Meter - Measures pH & Temperature in Solutions and Soil Solutions - Optimize Plant Health & Performance,White
  • Measures pH in nutrient solution (acid or alkaline) for precise up and down adjustment with lab quality glass probe; General uses include growing tent, swimming pool, drinking water, aquarium, fish tank, and brewing.Operating temperature : 0 - 50 °C, 32 - 122 °F.
  • This hydroponics tester has ATC that provides consistent reading regardless of any fluctuations in temperature; Calibration reminder; Durable design for repeated uses; Fully waterproof and floats in solutions
  • Double junction electrode has a longer lifespan compared to standard probes due to less contamination and is more accurate and reliable than comparable pens, test strips, drops, and more
  • Combine with ppm meters for full indoor garden nutrients monitoring in water and soil;
  • Fully waterproof - not just water resistant; Automatic temperature compensation for accurate readings everywhere

To get accurate readings, you must calibrate your pH pen. You can learn how to calibrate the Bluelab pH pen by following these simple steps.

When Should You Calibrate Your pH Pen?

It would help calibrate your pH pen at least once every month. Other times you are required to calibrate your Bluelab pH pen are:

  • Before using it for the first time
  • If the LCD does not display your calibration reminder anymore (after about 30 days of the first calibration)
  • If the measured value of pH is different than the expected value.
  • After the hydration and cleaning
  • After you change the batteries

Step-by-Step Instructions on How to Calibrate Bluelab pH Pen

Step 1: Clean and Hydrate Your pH Pen

Before you begin the process of calibration, you need to ensure that the pH pen is cleaned and hydrated. Follow the guide to learn how to clean and hydrate your Bluelab pH pen.

Cleaning the Bluelab pH Pen

To clean your pH pen, follow these simple steps.

  1. Remove the cap: Pull the cap and remove it. Or, if you have a different model, check if you need to unscrew the cap first.
  2. Take a jar or a plastic container and fill it with clean tap water. Now add a small amount of a mild detergent or the Bluelab pH Probe Cleaner to the water.
  3. Once the mixture is ready, dip your pH pen probe into the water and gently stir it. After dipping for a couple of minutes, rinse it under clean tap water to eliminate any traces of detergent. 
  4. If your pH pen requires cleaning of heavy contaminants, then use a soft-bristled toothbrush. While brushing, add a few drops of a mild detergent or the Bluelab pH Probe Cleaner on the brush.
  5. After brushing, rinse the pH probe under clean water.

Hydrating the Bluelab pH Pen

If your pH pen is not hydrated properly, it will not give accurate readings and might even break. To maintain the porous wick and the glass bulb of the probe, hydrate it in the Bluelab KCl solution. Follow this guide to learn how to hydrate the pH pen.

  1. Ensure that the pen is thoroughly cleaned before hydrating it.
  2. Take a small plastic container and add enough KCl solution to submerge the whole tip of the probe.
  3. Put your pen in the solution in an upright position.
  4. Let it sit in the solution for 24 hours until properly hydrated.
  5. Now remove the pen from the solution, wash it with clean water, and discard the used solution.

Important Tip: To avoid permanently damaging the probe, do not use reverse osmosis, distilled, or deionized water.

Step 2: Turn on the Power of the Bluelab pH Pen

Press the power button of your Bluelab pH pen and hold it until it turns on. Let the pen warm-up for a few seconds. Consult the manual of your pen to check how much time your pH meter requires to warm up.

Step 4: Prepare the Buffers for Calibration

You need buffers of various pH values to calibrate the Bluelab pH pen.

Important note:  The pH pen of Bluelab must always be calibrated to 2 points using fresh pH solutions of pH seven and pH four values. If the readings are supposed to be higher than 7 (alkaline), use a pH solution of pH 10 with a pH seven solution.

The buffer with a pH value of 7 is the neutral buffer. A lower pH buffer of value 4 is best for measuring acidic samples, while a higher pH buffer of 10 is best for alkaline/basic samples.

Step 5: Calibrate the Pen to pH 7

Now, to calibrate the pen, place it in the buffer solution of pH 7. Let the pen sit in solution and let the reading stabilize between a pH value of 6.6 to 7.5.

Hold the Cal button on the pen until the LCD shows “CAL.” The calibration sequence will start flashing zeros on the screen. Once the ‘0000’ stops flashing and stabilizes, the pen will display a value of pH 7.

How to Calibrate Bluelab pH Pen 2
Bluelab PENPH pH Pen – via

Step 6: Rinse Off the Buffer Solution

Rinse the probe with clean tap water after the sequence is completed and the pen is calibrated to pH 7.

Step 7: Calibrate the Pen to pH 4/ pH 10

Now place the pen probe in the pH four or pH ten-value buffer solution. The pH four buffer is acidic, while the pH ten buffer is basic/alkaline. Submerge the tip into the buffer solution of pH four and wait a few minutes until the readings stabilize between 3.6-4.5 pH.

After the reading is stabilized, hold the ‘Cal’ button on your pen until it displays “CAL” on the LCD. Once you release the button, the calibration sequence will start. After the “0000” on the screen stops flashing, the calibration sequence is complete. Now the LCD will display the value of pH four or pH 10.

Step 8: Confirm Calibration

Once you are done calibrating the Bluelab pH pen, a calibration message will appear at the bottom of the screen. This message indicates that the calibration has been successfully done.

After about 30 days, the message will disappear. It means that it is time to recalibrate the pH of your Bluelab pH pen.


To ensure the well-being of your plants and have a healthy harvest, maintaining the pH of the soil is of utmost importance. If the pH level of the growing medium is too low (acidic) or too high (alkaline), then your plants will not be able to absorb the required nutrients essential for their growth.

To maintain the pH level of your growing medium to optimal, you need to check it using your Bluelab pH pen regularly. And to ensure the readings are accurate and reliable, calibration is important. In this article, we have taught you how to calibrate the Bluelab pH pen. For any queries, leave a comment!