⚠️ Is a pH probe quality percentage reliable? (Beware of common errors)

When you calibrate your pH probe on an Avady device, a percentage is displayed (e.g. 82%, 74%, etc.).

👉 Many users think this figure precisely reflects the condition of the probe.
👉 In reality, this percentage can be misleading, notably due to several factors… including temperature, often underestimated.

In this article, find out why you shouldn’t rely solely on this percentage.

🌡️ 1. Temperature: the most underestimated factor

This is THE most important point.

👉 The theoretical slope of a pH probe (59.16 mV/pH) is only valid at 25°C.

➡️ In reality:

at 10°C → lower slope
at 30°C → higher slope

👉 So the formula used to calculate the % depends directly on temperature:

If temperature compensation is incorrect
or if the temperature probe is inaccurate

➡️ then the displayed percentage becomes wrong

⚠️ Concrete example

You calibrate:

once at 15°C
once at 28°C

👉 Without perfect compensation, you may get:

88% → cold
78% → warm

➡️ even though the probe hasn’t changed

👉 Conclusion:

❗ The percentage can vary solely due to temperature, not the probe’s actual condition.

🔍 2. The calculation doesn’t take everything into account

The percentage is based mainly on:

✔️ the slope (probe responsiveness)

But it often ignores:

the offset at pH 7
measurement stability
response time

👉 A probe can show 85% and still measure incorrectly.

🧪 3. Calibration solutions directly influence the result

The calculation depends entirely on your solutions:

expired pH 4 or 7 solution
contamination
poor storage

👉 Result:
➡️ slope miscalculated
➡️ misleading percentage

🧼 4. A dirty probe can make the percentage drop

A fouled probe:

reacts more slowly
gives an artificially low slope

👉 The % drops…

➡️ but the probe isn’t necessarily faulty

👉 After cleaning:
➡️ the % can rise significantly

⚡ 5. The percentage doesn’t reflect real-world behaviour

The calculation is done only during calibration.

👉 It doesn’t measure:

drift over time
variations in real pool water
stability

➡️ Yet in pools, these are the factors that really matter.

🧠 6. Each manufacturer has its own method

👉 There is no universal standard

So:

80% with Avady ≠ 80% elsewhere
different internal algorithms

➡️ Impossible to compare between brands

📊 In summary: why this percentage isn’t reliable

👉 It depends on:

temperature 🌡️
solution quality 🧪
probe cleanliness 🧼
the manufacturer’s algorithm ⚙️

➡️ It is therefore only an approximate indicator

✅ How to properly diagnose your pH probe?

👉 To know if your probe is truly reliable, check:

✔️ 1. The value at pH 7

→ close to 0 mV

✔️ 2. The gap between pH 7 and pH 4

→ close to 180 mV

✔️ 3. Stability

→ no fluctuations

✔️ 4. Response time

→ fast

💡 Pool expert tip

👉 If your percentage is low:

Clean the probe
Recalibrate with fresh solutions
Check the temperature

➡️ If the problem persists:
👉 the probe is probably at end of life

🛒 Need a reliable new pH probe?

On sonde-ph-redox-piscine.fr, we offer:

probes compatible with Avady
quality calibration solutions
expert technical advice

👉 Discover our probes here:
https://sonde-ph-redox-piscine.fr/

🔧 Conclusion

👉 The displayed percentage is useful… but insufficient

❗ It can vary greatly due to temperature, even with a probe in good condition

➡️ Never rely solely on this figure to judge your probe.

Tip:
A good diagnosis always relies on mV + real behaviour, not just a displayed %.

Reliability of Avady pH probe percentage: beware of common errors