If your pH readings are drifting, fluctuating, or don't seem quite right, it's usually a sign your probe needs cleaning, hydration, and calibration.
Over time, exposure to nutrient solutions and organic matter can leave salt residue, oils, and algal growth on your probe. This buildup can block the sensor, leading to inaccurate readings and incorrect nutrient adjustments that may affect nutrient uptake and overall plant health.
Hydration of your pH Pen or probe
Hydration is essential for accurate pH readings. If a pH Pen or Probe dries out, it can respond slowly, drift, or give unstable readings, and change the calibration curve, reducing accuracy. In severe cases, a dried probe can become permanently damaged.
Important: It is essential that you hydrate your pH Probe before calibration to ensure correct and accurate calibration.
Step 1: Hydrate before first use (or if the probe has dried out)
Remove the storage cap, stand the pen or probe upright in a clean plastic container, and add enough Bluelab pH Probe KCl Storage Solution to fully submerge the probe tip. Leave it to soak for 24 hours to properly rehydrate the glass sensor and reference junction. After 24 hours, rinse the probe tip with fresh water.
Step 2: Avoid soaking in pure water
Never store a pen or probe dry. Do not soak a probe in reverse osmosis, distilled, or deionised water. These waters lack ions and can disrupt the reference system, causing slow response and inaccurate readings.
Step 3: Stabilise before calibration (recommended)
After rehydration, rinse with fresh water and soak the probe tip in fresh pH 4.0 Calibration Solution for at least 10 minutes to help stabilise the sensor before calibration.
Step 4: Calibrate and store correctly
Once hydrated, calibrate to two points to confirm the probe is performing correctly. Finally, ensure the sponge inside the pen storage cap is damp (not dripping) with KCl Storage Solution, or fill the probe cap with enough KCl Storage Solution to cover the sensor, so the probe remains hydrated between uses.
Learn more about KCl Storage Solution here.
How to clean your Bluelab pH Probe
Your readings are only as accurate as the condition of your probe. Probe cleaning is one of the most important parts of owning and operating any Bluelab meter, monitor, or controller.
Consistent hydration, along with monthly calibration and cleaning, helps keep your pH readings accurate and reliable, whilst ensuring you get the longest lifespan out of your tool.
This cleaning guide applies to the Bluelab pH Pen, Bluelab Soil pH Pen, Bluelab Leap Probe and all other Bluelab Meters that use pH Probes with BNC connectors.
Cleaning your pH Probe is easy and won't take you long.
Step 1: Remove the storage cap.
Tip: Keep the cap upright so you don't spill the KCl Storage Solution.
Step 2: Rinse the probe tip in fresh water.
Step 3: Clean using Probe Cleaner or detergent. Once you've rinsed the probe, fill a small plastic container or cup with clean tap water and a small amount of Bluelab pH Probe Cleaner, and gently stir the probe tip in the mixture. When stirring, ensure you do not knock the probe against the side of the container, as this may damage the glass probe. Explore our Care Kits to get everything you need all in one box.
Step 4: Rinse well under fresh running water and ensure all traces of detergent have been removed.
Step 5: Remove heavy buildup if needed. If the probe has heavy contamination (for example dried nutrient salts, humus, organic oils, or fats), gently brush around the glass bulb using a few drops of Bluelab pH Probe Cleaner or a mild detergent (dishwashing liquid). Use a Bluelab toothbrush (from our Care Kits) or an extra soft children’s toothbrush, avoid using an old standard toothbrush, as the bristles are often too firm and can damage the glass bulb. Rinse thoroughly under fresh running water to remove all traces of the cleaner or detergent.
Once you have cleaned your pH Probe, make sure your probe is hydrated by soaking it for 2 hours, then it's time for calibration. Cleaning and calibration go hand in hand, so whenever you clean your pH Probe, recalibrate afterwards to ensure accurate readings.
Shop Care Kits here for everything you need to keep your probes in their best condition.
Why do I need to calibrate my pH Probe?
Calibration is essential because all pH Probes has slightly different characteristics from when it is new, and these characteristics change over time with use. When you calibrate your probe you compensate for these differences, ensuring your pH Meter gives accurate readings with your specific probe. Without calibration readings will drift, making them unreliable, leading to incorrect nutrient management and plant issues. To prevent his it is essential to calibrate every 30 days or more as your probe ages.
The sensor surface can develop a coating, the reference junction can become partially blocked, and the probe's can drift. Regular calibration corrects for this natural change by re-aligning the meter to the probe's current performance, helping you keep pH readings accurate and reliable.
When is calibration required for my pH Probe?
pH calibration is required before first use to ensure the first reading is accurate. It is also required when:
- The check mark/tick has disappeared from the screen. This happens every 30 days after the last calibration.
- The reading is different from what you expected.
- After cleaning and hydration.
- After changing the batteries.
Note: pH 7.0 and pH 4.0 solutions are required for calibration. You may also calibrate using pH 7.0 and pH 10.0 solutions if your readings are normally higher than 7.0 pH.
How to calibrate your pH Pen
Before you calibrate, make sure the probe is clean, hydrated, and rinsed. Turn the pH Pen on.
Step 1: Calibrate in pH 7.0 first
Pour a small amount of fresh pH 7.0 Calibration Solution into a clean container, then place the probe tip into the solution. For best practice, allow the pH probe to come to temperature in the solution before calibrating. Alternatively, use calibration solutions that are the same temperature that you will be measuring pH in. Tip: Always use fresh calibration solution and discard used solution. Do not pour used solution back into the bottle.
Why start with pH 7.0?
pH 7.0 is the neutral midpoint and the primary reference point for pH measurement. Calibrating at 7.0 sets the Pen's baseline (offset) before it adjusts accuracy across the rest of the pH range.
Press and hold the CAL button until 'CAL' appears on the screen, then release. The calibration indicator will flash while the Pen calibrates. Keep the probe in the solution while it flashes. When flashing stops and 'CAL' appears again, the first calibration point is complete.
Step 2: Calibrate the second point (pH 4.0 or pH 10.0)
Rinse the probe tip with fresh water and gently shake off excess droplets.
Place the probe into a fresh pH 4.0 or pH 10.0 Calibration Solution, depending on the range you normally work in:
- Use pH 4.0 for acidic readings (below 7.0)
- Use pH 10.0 for alkaline readings (above 7.0)
- Press and hold CAL until 'CAL' appears, then release. Leave the probe in the solution while the indicator flashes. When flashing stops and 'CAL' appears again, calibration is complete.
Calibration confirmation
If calibration is successful, a check mark/tick will appear on the screen. This check mark remains for 30 days, then disappears to indicate recalibration is due.
Note: Always calibrate to two points. A single-point calibration (pH 7.0 only) is not enough for accurate readings across your working range, and the Pen will not complete calibration properly unless both points are done.
Last quick tips for care
- Keep the probe tip moist. Add KCl solution to the well on the inside of the cap once a week, then refit the seal and cap securely over the probe tip. Don't let the probe tip dry out.
- Don't knock or drop the Pen. This may break the external glass bulb or internal glass tube.
- Don't touch the glass bulb with your fingers, as this will contaminate it.
- Don't plunge a cold probe into hot liquid or vice versa, as sudden temperature changes can crack the glass and permanently damage your pen.
- Don't soak the pen in RO (reverse osmosis) water. Although rinsing in RO water is acceptable but never soak in distilled or deionised water.
- Don't immerse in oils, proteins, or suspended solids that will leave a coating on the glass bulb.
- For long-term storage (e.g., between growing seasons), remove the cap and place your Bluelab pH Pen upright in a plastic container. Cover the probe tip with KCl storage solution to ensure constant hydration but make sure to check the container regularly and top up the KCl solution as needed.
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