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Thread: measurements different after reference test

  1. #1
    Join Date
    28.04.2022
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    31

    Default measurements different after reference test

    KHD director.jpg

    My new KHD SA doser is running for 3 weeks.

    Up to the first arrow, the measurements were comparable to the hanna. the latter measured between 8.0 and 8.2 throughout the photoperiod.
    It is of course the intention that I stop with the hanna, once I have confidence in the KHD.

    The day before the first arrow, the measurements were all 8.1. No problem, but normally there is a slightly declining trend during the day and a slightly rising trend at night. Which is normal of course.
    So I flushed the measuring cell 2x from GHL connect, nothing else.
    Then the measurements suddenly became 0.5 KH lower?

    The next 2 days the readings continue to decrease slightly. Since there is some variation in the calibration of the pumps in the beginning, I recalibrated all three pumps at the 2nd arrow. Pump 1 and 3 deviate 2ml and the reagent pump 0.2. So adapted.
    The Ph probe also suddenly checked, but it was ok. Both with 4 and 7 calibration fluid, the deviation was both 0.02. negligible.
    After the recalibration, the KH fluctuates around 7.2.

    So today at arrow 3, I ran some reference tests with KH 7.5.
    Results : 6.9, 6.7, 6.6 and 6.6.
    You can forget the first one, that is a mixture of aquawater/ref liquid.
    Actually, I think that is a far deviation from 7.5, but I will correct this via the correction factor. +13%.
    Then the very strange thing comes, back 2x the measuring cell rinsed and some aqua measurements made. 8.9, 8,6 and 8.7 .
    No other adjustments made, so the correction factor has been removed from arrow 4.
    Now the measurements are back 7.9, 7.8,...

    You would think that if you only run some reference tests and rinse the measuring cell, you would get the same value afterwards as for the ref tests? This is 0.8 difference. remains strange.

    Pump 1 empties its suction tube completely with the set value.
    Pump 3 certainly drains the measuring cell.
    There are no bubbles in the pipes of the 3 pumps.

  2. #2
    Join Date
    27.05.2015
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    Default

    Hello,

    What values do the KHD show when testing with the 7.5 fluid after the adjustment is made?
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  3. #3
    Join Date
    28.04.2022
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    Vinny, A few measurements later, the values where back the same as before the reference test. Measurements where quit stable and still are.

    2 days later i ran new reference tests (correction value was still 0). The same results as before 6.9,6.7,6.6 and 6.6. So my KHD is 0.9 off. I put a correction in place of 12%.
    But it's a brand new KHD.

    also pump 1 and 3 are squeaking a lot from day 2.
    I probably need to clean them? but that is very fast.
    Saterday or sunday i need to take a look at it. Before the weekend is impossible to do maintenance and test, busy at work.

    I looked trough the KHD subforum, because in the prsessure side of the reagent pump, there is an air bubble forming after 24 hour. It doesn't come from the reagent bottle, never saw a mini air bubble. The reagent bootle is not at vacuum, because there is an extra hole in the top. Temperature in the room is stable.

    Quit a few minor problems that needs to be solved, before i go further in the GHL upgrade (profilux 4e starter set).

  4. #4
    Join Date
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    Okay good, you can keep the 12% adjustment as-is. The purpose of this tool is to eliminate any discrepancies in the water sample tube volume and pump head calibration. As long as the results are consistent, that is what matters most. The end result can always be adjusted. If you were seeing wildly fluctuating numbers from test-to-test, that would be an issue in itself, but you're not seeing that so the KHD is working within the specified tolerances.

    You can add a very small amount of vaseline to the 3 white prongs which hold the 3 rollers in-place. This will make the heads quieter, however it does not mean one should go longer between cleaning intervals. Depending on how often you're testing, once every couple months may be enough for you.

    Regarding the air bubble, if the tubing is not pushed up enough on the tubing adapters is can allow air to make its way inside the tube. Make sure you have it pushed partly over the second step of the adapter.
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  5. #5
    Join Date
    28.04.2022
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    I still don't trust the KHD completely, certainly not to take control ans still not to adjust my KH manually.

    Most of the time it is pretty consistent, but the values doesn't goes the way i thought.
    My lights go on at 8 o clock, from 10u30 till 18u30 the lights are at their strongest. So i pressume the most KH consumption. Then the lights go down and at 22u they are out.

    I thought i would see a trend confirming this. the KHD measure 4 times a day.

    2 june i ran another testset with reference fluid and then it's consistent, 7.1, 6.9, 6.8, 6.8 and 6.8. I set the correction at 5%, not 10 because i still use my hanna checker as reference to correct my KH.
    I measure manually at 8u, 5 measurements at 7 days. values 7.8, 7.8, 7.9, 8.0 and 8.1. The KHD measurements at the same time, 7.8, 7.9, 8.1, 8.4 and 7.8.

    I included a trend of a week and a trend of the last 2 days.
    3 times i have a dip to 7.8, this morning it was 7.8 at 8 o clock. Normally i would expect that i would be at my highest KH peak in the morning hours.
    The fluctuations are not extreme, but i don't think i can let the KHD manage my KH doses.
    i dose with pump 4, 48 doses a day of 2.2 ml ATI essentials +.

    Do i expect to much of the KHD and is this a normal trend?


    KHD trend.jpg

    KHD 10-6.jpg
    Attached Images Attached Images
    Last edited by Nico F.; 12.06.2022 at 19:45.

  6. #6
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    The trend depends on your specific tank and KH consumption patterns. Typically consumption increases just before the lights turn ON, but this is not always the case as every tank will have a different "norm". If you're doubting the KHD results, you can always test it with the 7.5 reference fluid 3 times back-to-back. If the results are consistent, the KHD is providing the correct values. It would also help to check the water sample filter as these do become clogged over time and when it does happen, it can restrict the actual water sample used for the test, therefore skewing the KH end results.
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  7. #7
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    Quote Originally Posted by Vinny View Post
    The trend depends on your specific tank and KH consumption patterns. Typically consumption increases just before the lights turn ON, but this is not always the case as every tank will have a different "norm". If you're doubting the KHD results, you can always test it with the 7.5 reference fluid 3 times back-to-back. If the results are consistent, the KHD is providing the correct values. It would also help to check the water sample filter as these do become clogged over time and when it does happen, it can restrict the actual water sample used for the test, therefore skewing the KH end results.
    The test with the reference fluid are ok, low but that is adjusted with the correction factor.

    The problem is probably that over a few days time, there's a little air bubble forming just at the outlet side of the reagent dosing pump.

    A few days or maybe a week it produces values that probably are in range of the true value, without seeing a returning pattern. Which I would expect, because my KH dosing values are stable.
    I recalibrated the pumps probably 5 times, never a big deviation.
    Sample size is 100 ml.
    The inline sample filter is ok. I presume that the measured sample tube value is also correct, because when a measurement is done and the sample tube is pushed empty by the sample dosing pump, it’s just getting emptied, maybe 2 bubbles of air are pushed out, before the pump stops.
    The vent tube is empty and above the waste water level, same for the waste water tube.
    I still have a problem that a little air bubble is formed, right at the outlet of the reagent pump. It takes a few days. So the most probably cause for my problem.
    I don’t know why the air bubble is forming.
    I replaced the PVC flex tubing with new PVC flex tubing, they are pushed to the end on the connection pieces of the dosing pumps.
    The reagent bottle cap has an extra little hole, so under pressure is not possible.
    The suction side flex PVC tube to the reagent pump is straight to the pump, no turns. Reagent tube Length is about 33 cm and fully submerged.
    The room temperature is pretty stable, between 20 to 22°C.
    I already used 2 bottles of GHL KH 7.5 reference. The KH director produces stable values, but not with in the expected 7.1 to 7.9 range.
    The last set was 7.1, 6.9, 6.8, 6.8, 6.8. So this I can adjust whit the correction factor. But it should be in range because the PH probe is 2 months old, I bought the KHD, SA unit brand new.
    Does someone has another idea why the little air bubble is forming, right at the outlet of the reagent dosing pump? I can’t see any “micro” bubbles in the suction side.

  8. #8
    Join Date
    08.08.2022
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    Hello,

    I have exactly the same problem of measuring the reference KH 7,5 at about 1 Dkh below.
    I don't have a problem with bubbles in the reagent tube but the sample tube is not properly drained.

    Have you found a solution?

  9. #9
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    The solution is to use the adjustment tool. As long as the results are consistent with itself, it is OK to use that feature.
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