About this article

This article will provide you with tips and troubleshooting guides so you can get the highest accuracy and reliability from the KH Director. If you still require assistance, please use the ticket system so we can provide further support.

Achieving maximum accuracy

In order for the KHD to give you the most accurate results possible, we highly recommend the following…

• Calibrate the dosing pump heads using a graduated cylinder or digital scale.
• Calibrate the KHD probe by following the instructions in the manual and/or how-to video. For maximum accuracy, we recommend calibrating every 4 weeks.
• Keep the tubes as short as possible. The length of the reagent tube from the pump head to the reagent bottle should be kept under 70cm (27.5 inches).
• In order to avoid air bubbles in the reagent tube, use the Flex PVC tubing that was included in the KHD product box.
• Keep the vent tube ABOVE water at all times!
• The amount you enter into the Sample tube volume field MUST be 100% correct. An incorrectly entered amount will result in skewed KH test results!

KHD results vs. other test kit results

Due to the differences in testing technology between the KHD and traditional test kits, we do not recommend using these kits as a baseline for testing the accuracy of your KH Director.

WHY?
Our findings and observations from many customers have shown that traditional test kits can be up to 2°dkH apart from the measured value of the KHD. These kind of differences can be caused by various factors which the KHD does not have to worry about.

For example, fingerprints on measurement vial, dust or solids in sample, varying perception of ending-color, varying perception of amount in syringe, age of reagent liquid or powder, etc. These factors are product and user dependent.

The KHD on the other hand uses lab-grade protocol to perform each test. It does not rely on the user manually measuring or interpreting results, this is all done mechanically. As long as the instructions and the tips on this page are properly followed, the KHD will provide maximum accuracy and consistency.

How to verify the accuracy of the KHD

Using a traditional test kit as a base line for verifying KHD accuracy is not recommended for the reasons above. In order to fine-tune your KHD, we recommend using the GHL KH reference solution.

This reference solution will be the most effective method for adjusting your KH end-results because it is a lab grade solution that remains at a stable (7.5°dkH w/ +/- 0.2 tol.) KH value instead of the varying KH values and factors introduced by traditional test kits.

Here’s how to use the GHL Reference Solution:

1. Take the KHD water sample tube out of your tank and place it in the reference bottle
2. Run at least 3 KH tests back-to-back.
3. By the 3rd test, your KHD should be displaying results within the acceptable range considering all tolerances (KHD, reference and reagent) — 7.1°dkH – 7.9°dkH

If the test results are outside of this range, check your pump calibration, KHD tubing setup (no air bubbles), and use this page as a guide for finding the cause of the discrepancy.

Using the KHD adjustment feature

The KHD offers the option to adjust the end-result of your KH test results. This feature will modify the KHD’s lab grade accuracy and should only be used if you would rather see the KHD result match the outcome of another testing instrument.

An adjustment of up to +/- 30% is possible.
The feature can be found in the KHD settings page.

Here is the formula for calculating the percentage adjustment value:
(7.5 – KHD value) / KHD value = Percentage adjustment

Example: If you run 3 consecutive KHD tests and the average of those tests comes to 8.0…apply the 8.0 figure to the formula to get an adjustment of – 6%.

Example 2: If the average test comes to 7.0…apply the 7.0 figure to the formula to get an adjustment of 7%

Fluctuating test results

This section does not apply to the normal fluctuating KH values that naturally occur in reef aquariums. Here, we will focus on a scenario where you are experiencing fluctuating test results from your KHD.

For example, testing 3 times in a single day with results of 4.5, 10.9, 6.9.

There are several possibilities which can cause this kind of behavior:

• Measurement cell is not emptied properly after a KH test
• Measurement cell is not rinsed properly before a KH test
• Air bubbles somewhere in water sample and / or reagent tube
• Dirty water sample filter
• Timing of KH test vs. KH dosages; if KH test occurs shortly after a KH dose and the tubes are near each other, the KHD may take-in a water sample with concentrated KH

TIP: Use the “Flush measurement cell” function then run a few back-to-back tests. The results should be consistent with each other. If further tests result in varying results, the problem may be caused by the above possibilities.

SOLUTION: Calibrate dosing pump heads

Possible cause: Sample tube volume is NOT correct
SOLUTION: Remeasure the length of the water sample tube including the filter. If need be, you can manually measure the tube volume by disconnecting the sample tube from the KHD and completely priming the tube with tank water. Once both ends of the tube is filled, manually run the pump and have it drain into a measuring instrument. The amount that was dispensed from the tube is what you should have entered into the Sample tube volume field.

Possible cause: Vent tube does not hang freely or is submerged in water
SOLUTION: Inspect tube

Possible cause: Sample and/or waste water pumps are not calibrated correctly
SOLUTION: Calibrate this pump heads

How to verify probe accuracy

If you are unsure whether the probe needs calibration or not, you can follow these steps to verify the accuracy of your KHD probe.

1. Run Empty measurement cell function in KHD settings to drain all fluid from inside the device.
2. Remove the probe from the KHD and dip the probe in pH 4 calibration fluid, let it sit for 4 – 5 minutes.
3. Go to the KHD settings page and look at the Current pH value field located in the Diagnosis section. The pH value displayed should be within +/- 0.1 of the calibration fluid value. The acceptable range for pH 4 fluid is 3.9 – 4.1  If the value is outside of this range, stop here and calibrate the probe.
4. Wipe and dry the probe, then let it sit in pH 7 calibration fluid for 4 – 5 minutes.
5. Observe the displayed pH value. The pH value displayed should be within +/- 0.1 of the calibration fluid value. The acceptable range for pH 7 fluid is 6.9 – 7.1  If the value is outside of this range, stop here and calibrate the probe.

“Titration takes too long” error

This error will show up if the KHD probe does not detect enough of a change in the pH value of the water sample. During a KH test, when the reagent is added to the water sample, the probe is given a certain amount of time to reach a target pH value. If this target is not reached within the allowed time, you will see this error.

There are several reasons why you may be seeing this error. The causes and solutions for each are listed below.

Possible cause: Reagent is empty or taking in large air bubbles
SOLUTION: Top up with new reagent and use the “Vent internal reagent tube” function before testing again.

Possible cause: Internal circulation (mixing) pump is not running.
TIP: If you are close enough to the KHD, you should be able to hear the pump running during a measurement.
SOLUTION: Contact service by creating a support ticket

Possible cause: Internal reagent tube is clogged or pinch valve is not opening
TIP: Within seconds of starting a measurement you will hear a “pop”-like sound from the KHD. This the sound of the valve opening and closing.
SOLUTION: Contact service by creating a support ticket

Possible cause: Measurement cell is not sufficiently filled with sample water. As a result the pH probe is not fully submerged
SOLUTION: Calibrate water sample and waste water pump heads

Possible cause: pH probe is defective
SOLUTION: Calibrate the probe. If calibration fails, replace the pH probe.

Possible cause: Reference fluid is being used instead of KHD reagent fluid
SOLUTION: Check the label on the bottle and replace if necessary.

“Leakage alarm” error

The KHD has an internal leakage sensor which is a safety mechanism that shuts down the system in case a leak is detected.

If this error occurs, the device must be powered OFF immediately and must not be used.

SOLUTION: Create a support ticket

KH results are unusually low

If you are noticing that your KHD is reporting lower than expected values, it is possible that the water sample filter may be dirty or clogged.

SOLUTION: Inspect the water sample filter and replace.

If the numbers are still unusually low, do the following:

• Re-calibrate KHD probe
• Test with the 7.5dkH Reference Solution for highest accuracy

KH results reading (0)

There are several reasons why the KHD may be reading 0 dkH as a measurement result.
If you notice this behavior, do the following inspections:

Is your water sample being pumped into the KHD?
Do you have enough reagent fluid in the bottle?
No air bubbles in the water sample and reagent tubes?
Are the dosing pumps calibrated correctly?

Observe the measurement process
Start a new KH measurement and observe the process to get a better understanding of what may or may not be happening.

If you don’t see anything suspicious, check the KHD pH probe:

• Calibrate the KHD probe
• Dip the probe in pH 4 fluid and see if you get 4.0 as a result in the Current pH-value field of the KHD settings page
• Dip the probe in pH 7 fluid and compare results

KHD reagent pump is NOT turning ON during test

If the KHD reagent pump is not turning on during the test, it is possible that the KHD sensor needs to be cleaned and recalibrated. A dirty KHD probe may also result in skewed pH values which ultimately affect the KHD’s testing process.

For example, if there is “growth” on the sensor tip, this will cause the reported pH value to be low. When the KHD begins the reagent adding phase, it looks for a steady pH value before calculating the KHD value. With a blockage, this will register as a false steady pH value, therefore preventing the assigned pump head from running because the probe tells the KHD that no more reagent needs to be added.

SOLUTION: Inspect the KHD probe, clean and recalibrate.