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Thread: Measurements fluctuating

  1. #1
    Join Date
    05.08.2022
    Posts
    1

    Default Measurements fluctuating

    Hi,
    I have had a KHD since the last February and since then, I have not really succeeded to obtain stable measurements from one day to the other.
    Here is the setup and what I did:
    Firstly, I read carefully the installation instruction, used the inline filter, all tubes are under 35cm, the vent tube has the head out of the water, making sure the sample tube was not in a bubble area of the sump, etc...
    I also used the reference solution to validate my setup and obtained 7.6-7.5dkh after 5 consecutive measurements as advised, so I guess my setup is ok right?
    I also tried to move the sample tube to the next sump, away from the Alkalinity doser, and still got big fluctuations from one day to the other.
    The KHD is doing a single measurement every day at exactly the same time so it should always be at the same point in the Alkalinity consumption cycle from the reef... I guess...
    So far, I could never really rely on its measurements to set the Alkalinity dosing, I ratter check with two other tests (hanna and redsea) which are not giving exactly the same results but the results are
    really stable from day to day and it is what I'm expecting as my system is over 500g and 7 years old with a lot of SPS and few LPS and all are healthy and colorful.
    My readings from other tests fluctuate by about 0.2dkh every 2 weeks and I slightly modify the alkalinity daily dose at this time.
    Here is an example of the KHD dkh readings sequence at the same time every day for 21 days:
    9.5
    11.9
    9.4
    11.5
    11.5
    11.3
    11.3
    11.7
    10.1
    10.0
    10.1
    10.2
    9.8
    9.4
    9.4
    9.2
    9.2
    10.2
    11.0
    10.1
    10.6
    11.1
    ...
    During all this time, the alkalinity dosing amount/day was the same and my other test kits were reading stable results.
    Any good advice is welcome!
    Please don't hesitate
    Best regards

  2. #2
    Join Date
    27.05.2015
    Posts
    2,382

    Default

    Hi there,

    What KH results do you get if you run 3 tests back-to-back?

    Since the probe has been used since Feb 2022, that would make the probe about 6 months old. How many times has the probe been calibrated in that time?

    Have you checked your water sample filter? Maybe it is getting clogged and is affecting the actual sample amounts being used for each test.
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