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×Tips
CLF Probe - Correct Installation & Answers to Common Questions
The Aseko CLF probe is a reliable tool for measuring free chlorine in water. Correct installation, accurate calibration, and careful maintenance ensure precise measurements for many years.
Here's a practical summary - from answers to frequently asked questions to useful tips from real-world practise.
The CLF probe measures the concentration of free chlorine (HOCI and OCI) electrochemically. A chemical reaction at the cathode generates an electric current, the value of which corresponds to the amount of free chlorine in the water. Thanks to the use of high-quality materials, the probe's lifespan is many times longer than that of standard glass or plastic probes. 
Key steps from the manual
1. Filling the membrane module with electrolyte
Fill the membrane module with the original electrolyte up to the mark. Gently tap it to release any trapped air bubbles.2. Mounting the probe
Screw the probe into the module. While doing so, gently hold the membrane on the bottom side of the module with your index finger. Tighten until you feel the probe tip touching the membrane. After tightening, the membrane should be slightly convex. If there is no direct contact, the probe will not measure correctly. Excess electrolyte will drain through a micro-vent - never cover or seal this vent!3. Activating the probe
Before placing it in the flow cell, shake the probe (like a thermometer). Insert it into a flow cell and connect the cable. Let the probe stabilise for at least one hour after connection - this allows the signal to settle in the new electrolyte. Once the signal is stable, proceed with calibration.
Probe calibration
Assign a specific free chlorine concentration in mg/L (ppm) to the current mV signal. Since the mV signal is not linear to chlorine concentration, you must calibrate to the value you want to maintain in the pool - or a slightly higher value. Never calibrate to a lower value.
Calibration steps
- Check the pH of the water - it must be between 6,8 and 7,4. Outside this range, the probe may show inaccurate or false values. Adjust pH first if needed.
- Measure free chlorine using a digital photometer (DPD1 test). Take the sample from a point after the pump and before the filter, as close as possible to the probes. This prevents errors caused by sampling from the pool where the water may not be fully mixed.
- If the photometer reading and the probe display differ by less than 0,2 ppm, calibration is not necessary.
- If the photometer reading is equal to or higher than your target free chlorine level, enter this value in the CLF probe calibration menu. If the photometer reading is lower, first raise the free chlorine level in the water.
Example of correct calibration
When calibrating the CLF probe, compare the value shown on the controller with the value measured by the photometer. If your target is 0,6 ppm, the controller shows 0,6 ppm, but the photometer reads only 0,3 ppm, manually increase the target value on the controller to 0,7 ppm and wait until this value is stably displayed. Then mesure again with the photometer. If the photometer reading reaches 0,7 ppm or more, enter this valuein the CLF probe calibration menu. If the reading is still below the target, repeat the process.⚠️If you calibrate to a low value (e.g., 0,3 mg/L) and then set a higher target (e.g., 1,2 mg/L), you risk overdosing chlorine.
Most inaccuracies during CLF probe operation are caused by poor calibration. Always ensure stable connections, precise manual measurements, and calibrate to the same or a higher value than your target.Common questions from the field
The probe stops measuring and, even with at least 0,5 ppm chlorine present, shows values below 20 mV. Proceed as follows:
Check for cyanuric acid
Make sure the pool water contains no cyanuric acid stabiliser. It often enters the water unnoticed as part of cheaper chlorine tablets or low-quality shock treatments. Cyanuric acid reduces chlorine effectiveness, disrupts probe readings, and prevents accurate control. If present, dilute the pool water by partially draining and refilling with fresh water. Use high-quality chlorine shock, such as PoolHelp, which is fully compatible with ASIN AQUA systems and maintains measurement accuracy.Replace the electrolyte
Follow the same procedure as when putting the probe into service.Replace the membrane module
Damaged or contaminated membranes prevent correct probe function.Pro tip
Measure the probe resistance with an ohmmeter. The resistance between the connector and the outer ring of the probe must be exactly 1 MΩ.Regular maintenance extends lifespan!
> During downtime (e.g., winter), remove the probe, clean it, and store it dry at room temperature.
> If the probe shows errors or cannot be calibrated, replace the electrolyte or the entire membrane module.
> Always rinse the membrane and probe body with clean water - keep the probe connector dry!
What to avoid
Do not use cyanuric acid - it completely disrupts chlorine effectiveness and probe measurements.
Do not cover the micro air bleed hole - even after screwing the probe into the module, never seal or block the membrane, as this may cause damage.
Do not install sampling after the filter with return after the pump - this may cause the membrane to lose contact with the probe tip, resulting in inaccurate readings and overdosing.
Install sampling points for calibration as close to the probes as possible - sampling after filtration or directly from the pool can cause misleading results.
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