Behind every accurate pH measurement is a deceptively small yet powerful component: the glass bulb. Found in your pH pen or probe, this fragile membrane is the unsung hero of hydroponics, horticulture, and controlled growing environments.
Download this as a printable Factsheet here
In this guide, you'll learn:
What is a pH Probe and How Does It Work?
A pH probe measures the concentration of hydrogen ions (H⁺) in a solution to determine its acidity or alkalinity. At its core lies the glass bulb, a sensor that interacts with the solution at a molecular level to produce a small voltage, which is then translated into a pH value.
Anatomy of a pH Probe
The diagram below shows a typical double-junction pH probe, highlighting key components:
Glass pH sensing membrane
Hydrated gel layers (inner and outer)
Reference solution and electrode
Internal and external tubes
pH electrode wire (Ag/AgCl)
Glass is the material of choice for pH sensing due to its ability to:
Enable ion exchange for fast readings
Interact precisely with hydrogen ions
Maintain structural integrity while remaining delicate
Why the glass bulb matters
The glass bulb may look simple, but it’s responsible for:
Detecting hydrogen ions that alter voltage depending on the solution's acidity
Translating that signal into accurate pH readings
Responding rapidly to changes in solution thanks to its ion-permeable glass membrane
Without proper care, this tiny sensor can quickly lose accuracy or fail altogether.
How to Store Your Probe Correctly
Storage is the most critical factor in extending the life of your pH probe.
Do:
Always store the probe in a specialized pH storage solution
Keep the glass bulb moist and submerged
Ensure the storage cap or container fully covers the bulb
Don’t:
Store in RO, distilled, or deionised water, these lack ions and can leach the probe’s internal solution
Let the bulb dry out, even briefly
Improper storage leads to damaged junctions and inaccurate readings.
Cleaning Your Probe Safely
Proper cleaning ensures your pH probe remains responsive and accurate.
After Each Use:
Rinse the probe tip in clean tap water to remove salts or nutrients
For Deep Cleaning:
Use a dedicated pH probe cleaner
Gently scrub with a soft toothbrush
Soak in KCl or pH 4 solution before calibration
Avoid abrasive tools or harsh chemicals; these can permanently damage the sensitive gel layer.
Handling and Calibration Tips
Your probe is a precision instrument. Handle and calibrate it accordingly.
Handling Guidelines:
Never touch the glass bulb directly; finger oils can distort readings
Always hold the probe by the body
Avoid dropping, tapping, or shaking the probe
Calibration Best Practices:
Calibrate at least every 30 days, or more often with frequent use
Use fresh calibration solutions
Always perform a two-point calibration with pH 4 and pH 7
If your probe refuses to calibrate, it may be time to replace it.
Troubleshooting a Failing Probe
Even with care, probes degrade over time. Here’s how to diagnose issues:
Warning Signs:
Sluggish response times
Inconsistent or drifting readings
Reads pH 7 in all solutions
Physical damage (cracks, chips)
Simple Test:
Place the probe in a pH 4 solution
If it reads pH 7 and won’t calibrate, the bulb may be broken
Recommended Products for Probe Care
Bluelab offers a full suite of solutions to help you care for your pH equipment:
KCl Storage Solution – Keeps the bulb hydrated and functional
Probe Care Kits – Include cleaning tools, solution, and how-to guides
Calibration Solutions (pH 4 & pH 7) – Essential for maintaining accuracy
Explore the full range at bluelab.com, or scan the QR code on your product to visit the support portal.
Frequently Asked Questions
Can I store a pH probe in distilled water?
No. This will damage the reference junction. Always use a pH storage solution.
How often should I calibrate my probe?
At least once every 30 days, or more frequently with daily use.
What does it mean if my pH probe always reads 7?
It may be broken, especially if it shows 7 even in calibration or acidic solutions.
How do I clean a pH probe correctly?
Rinse after use; for deep cleaning, use probe cleaner and soak in KCl or pH 4.
How do I know when to replace my probe?
If it won’t calibrate, responds slowly, or has physical damage, it’s likely time to replace it.
Final Tip
Proper care extends the life of your pH probe and ensures the accuracy you depend on for successful growing. Treat it like the scientific tool it is, and it will reward you with reliable performance every time.