Cause

Most measurement problems trace back to one of three physical installation errors rather than a software or hardware fault:

• Wrong tubing material: Standard silicone tubing used for the Reagent line instead of the provided Flex-PVC. Silicone allows air diffusion, which shifts titration results over time.
• Vent tube kinked or submerged: A blocked vent tube prevents proper pressure equalization inside the measurement cell. If the open end is submerged in the waste container, waste water can be siphoned back into the device during the pump-out phase, risking contamination.
• Reagent and Reference solution mixed up: The KH Reagent is required for every titration; the KH Reference solution is only used to verify accuracy (see Verification of Measurement Accuracy below) and will cause the titration to fail if dosed by mistake.

Solution

• Check tubing material: Confirm that Flex-PVC tubing is used along the entire Reagent path (bottle → pump → KH Director).
• Check the vent tube: Ensure it is unobstructed and its open end remains above the waterline of the waste container. If you notice water inside the vent tube, run the “Empty measurement cell completely” function and re-check your Sample and Waste pump calibration.
• Check bottle labels: Verify labels before connecting or refilling the Reagent pump.

Cause: Air bubbles in the reagent line

Micro-bubbles trapped in the reagent line are the most common cause of jumping or inconsistent values. This is often caused by using improper tubing or loose connections.

Solution

• Use Flex-PVC: Ensure the entire reagent path uses the provided Flex-PVC tubing to prevent air diffusion.
• Vent the system: Use the Vent internal reagent tube function until absolutely no micro-bubbles are visible in the line.
• Airtight connections: Check all tube connections and ensure the reagent bottle cap is fitted correctly.

Cause: Incorrect Sample tube volume

If the volume of the sample tube (from the water source to the pump) is not correctly defined, the titration cell will not contain the precise amount of water needed for a correct analysis.

Solution

• Measure accurately: Determine the exact length of your sample tube in cm.
• Use the Software Calculator: Enter the length into the Tube volume calculator within the KH Director settings. Do not guess the volume; let the software calculate it based on the tubing’s internal diameter.
• Filter Volume: Ensure the Add inline filter volume option is checked if you are using the GHL particle filter.

Cause: pH sensor aging or failure

The KH Director relies on a precise pH reading to determine the titration endpoint. If the sensor is failing, the results will drift or become erratic.

Solution

• Check Calibration: Perform a 2-point calibration using pH 4 and pH 7 buffer solutions.
• Replacement: If the sensor can no longer be calibrated or the ADC values are too close together, the sensor must be replaced.

Cause: Electromagnetic Interference (EMI)

High-voltage cables or equipment near the KH Director or its sensor cable can distort the sensitive pH signal, leading to fluctuating results.

Solution

Route the pH sensor cable away from power cords for large pumps, heaters, or LED ballasts. Ensure the plug is fully inserted into the back of the KH Director.

Cause: Reagent delivery issues or wrong fluid

Reagent delivery failure due to air pockets or incorrect pump calibration, accidental use of GHL KH Reference instead of Reagent, or excessive dilution from residual water in the measurement cell.

Solution

• Check Fluid Type: Ensure you are using KH Reagent and not GHL KH Reference solution.
• Priming: Verify that the reagent line is fully primed and free of air gaps.
• Pump Speed: The Reagent dosing pump must be calibrated and operated at Speed 0.

Cause: Sample/Waste pump calibration or cell drainage

If the measurement cell is not completely emptied after the previous test, or if the Sample pump delivers an incorrect volume, the titration will fail.

Solution

• Verify Calibration: Check that the Sample and Waste pumps are calibrated correctly and set to Speed 3.
• Clear the Cell: Run the Empty measurement cell completely function to ensure a dry start for the next measurement.

Cause: pH sensor problem

An aging or malfunctioning pH sensor may react too slowly to the reagent addition, preventing the system from identifying the endpoint within the safety timeframe.

Solution

Perform a fresh 2-point pH calibration. If the response time during the calibration (moving between pH 4 and pH 7) is noticeably slow, the sensor is likely failing and should be replaced.

Comparison with manual test kits

Manual drip-test kits have significantly higher tolerances and are prone to subjective interpretation (color change) and user error. They are not a reliable benchmark for the KH Director’s lab-grade accuracy.

Trust the KH Director’s trend over single manual measurements. If you suspect an inaccuracy, always perform a reference test using the GHL KH Reference solution.

Performing a Reference Test

Using the GHL KH Reference solution (7.5 °dKH) is the only valid way to verify the device’s absolute accuracy.

Procedure:

1. Remove the Sample water tube from the aquarium/sump.
2. Wipe the end of the tube dry and place it into the Reference solution bottle.
3. Run at least 3 KH measurements back-to-back.
4. By the 3rd measurement, the result should fall within the acceptable range of 7.1 °dKH – 7.9 °dKH, accounting for the combined tolerances of the KH Director, the reference solution, and the reagent.

After testing:

1. Remove the tube from the bottle, wipe it dry, and reinsert it into the aquarium/sump.
2. Run the “Flush measurement cell” function 1–2 times to clear any residual reference fluid from the lines before resuming the normal measurement schedule.

Note: After switching back to aquarium water, it can take up to 3 measurement cycles before the displayed KH value again accurately reflects your tank’s actual alkalinity..

Cause: Buffer handling or contamination

While older buffer solutions can be used, contaminated buffers will cause calibration failure.

Solution

• Proper Handling: You may dip the sensor directly into the buffer bottles, but you must wipe the sensor tip dry with a clean tissue before moving it between fluids to prevent cross-contamination.
• Fresh Buffers: If in doubt, use a fresh, uncontaminated buffer solution.

Cause: Hardware fault (Port vs. Sensor)

The issue could lie with either the pH sensor itself or the port on the KH Director.

Solution

• Cross-Test (Port): To determine if the port is faulty, try calibrating a different GHL pH sensor (e.g., from a ProfiLux) at the KH Director port.
• Cross-Test (Sensor): Alternatively, try connecting and calibrating the KH Director sensor at a ProfiLux pH port.

Cause: Electromagnetic Interference (EMI)

High-voltage cables or equipment near the KH Director or its sensor cable can distort the sensitive pH signal during the calibration process.

Solution

Route the pH sensor cable away from power cords for large pumps, heaters, or LED ballasts. Ensure the plug is fully inserted into the back of the KH Director.

Cause: PAB communication or assignment issues

The KH Director cannot trigger its pumps if the Doser is not correctly assigned or the PAB cable is loose.

Solution

Verify PAB assignment in GHL Connect app or GHL Control Center. Check that the PAB cables are firmly plugged in and that the Doser’s status LEDs indicate a normal state.

Cause: Low Reagent fluid level

If the controller detects that the calculated fluid level for the reagent is too low, it will prevent a measurement from starting to avoid drawing air into the measurement cell.

Solution

Check the fluid level in the GHL Connect app or GHL Control Center. After refilling or replacing the reagent bottle, you must manually refill the fluid level in the software to enable the measurement function again.

Cause: No Doser assigned via PAB (for ProfiLux Controllers only)

The KH Director does not have its own internal pumps and relies entirely on a GHL Doser for fluid delivery. If no Doser is assigned via PAB, the system cannot initiate a measurement.

Solution

Ensure that a GHL Doser is correctly connected via PAB and assigned in the system configuration. Without a valid PAB assignment, the KH Director lacks the hardware (pumps) necessary to perform a measurement cycle.