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Thread: Conductivity Probe values drifting down

  1. #11
    Join Date
    18.02.2009
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    Kaiserslautern
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    7,710

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    there is a simple test to check if the measurement is correct:

    1. do a precise calibration - fluid bottle for some hours in tank, use the tank water temp. as reference during calibration

    2.leave the bottle in the tank: put the probe into the fluid (which has tank temp.) and check if it shows 50.0mS (+/-0.2 is OK and normal)

    of course the tank temp. probe must be used for compensation
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  2. #12
    Join Date
    19.02.2017
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    18

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    ok perfect..thank you matthias i'll let you know.

  3. #13
    Join Date
    21.02.2017
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    24

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    - conductivity probe is brand new
    - Calibrated, and re-calibrated following manual (with floating 50ms fluid in tank water for several hours to ensure equal temp)
    - no algae or bubbles on probe (it's brand new; plus it's in my sump on a probe holder right next to the temperature probe. The skimmer is in a chamber downstream of probe)
    - consistently seeing a downward trend in my conductivity reading. I have the past 18 hours of data I can share, which shows "part" of the downward trend. I havn't figured out a way to compile all the previous data saved into one long graph.
    - temperature is stable with +- .5 degree F

    Screenshot (384).jpg

  4. #14
    Join Date
    21.02.2017
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    24

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    - Took probe and pulled it out of the water (for 2 seconds)
    - placed probe back in sensor holder
    - waited 5 minutes (in case any temperature difference from removing from water for 2 seconds)
    - new reading of conductivity is 35.5 PSU, which is 1.6 PSU (parts per thousand) higher than before removing from water for 2 seconds.Screenshot (386).jpg
    - Awaiting new graph data (going to record over 24 hour period, and show drifting effects)

  5. #15
    Join Date
    18.02.2009
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    Kaiserslautern
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    Quote Originally Posted by dawsokj1988 View Post
    - Took probe and pulled it out of the water (for 2 seconds)
    - placed probe back in sensor holder
    - waited 5 minutes (in case any temperature difference from removing from water for 2 seconds)
    - new reading of conductivity is 35.5 PSU, which is 1.6 PSU (parts per thousand) higher than before removing from water for 2 seconds.Screenshot (386).jpg
    - Awaiting new graph data (going to record over 24 hour period, and show drifting effects)
    This is all very interesting doesn't tell us much.
    Please let us stay with the measured base unit (mS), all other values are calculated.
    Put for a test the probe into the fluid bottle which has been floating all the day in your sump (where the probe is). This reading (must be 50mS +/-0.2) is interesting.
    I assume the calibration fluid was floating in the sump before calibration since the probes are there, too.
    No support or warranty issues over PM! Please send PMs to the moderators only if you have general problems with using the forum! Thanks for helping us to keep the support efficient.
    Kein Support oder Reklamationsabwicklung über PM! Bitte senden Sie an die Moderatoren nur PMs bei allgemeinen Problemen mit der Verwendung des Forums! Danke dass Sie uns dabei helfen, den Support effektiv zu gestalten.

  6. #16
    Join Date
    19.02.2017
    Posts
    18

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    Hi guys.. i recalibrated yesterday (after update GCC and P4 new firmware ) all process is done correctly with floatind bottles and controlled temperatures.

    Yesterday 35.1 PSU

    this morning 34.3 PSU

    ..

  7. #17
    Join Date
    21.02.2017
    Posts
    24

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    I just tested a theory, and it worked.

    The issue I believe is microbubbles. This explains why pulling it out of the water for 2 seconds and putting it back in would correct the conductivity reading.

    I tested it by allowing the probe to sit in the sump for 12 hours. Over this 12 hours the conductivity drifted from 54ms to 49.2ms. I then took a turkey baster and blew the probe with some water (without pulling it out of the water), and the readings corrected to 54ms.

    I'm going to move the probe in front of the inflow and see if the high flow will eliminate the microbubbles (thus confirming the theory).

  8. #18
    Join Date
    21.02.2017
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    24

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    Well I moved the probe to in front of the inflow area (with high flow), and I'm still having the same issue. If it is microbubbles, how is this solved? I'm reading posts of people using different conductivity sensors 2 cm away from the pl4 sensor for reference. The pl4 sensor is giving erratic readings, while the other sensor is giving normal readings. Is it just the design of the probe that makes it highly susceptable to microbubbles?

  9. #19
    Join Date
    23.10.2016
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    55

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    Quote Originally Posted by dawsokj1988 View Post
    Is it just the design of the probe that makes it highly susceptable to microbubbles?
    I do not know. Matthias has said in another thread, that a lot of people are using the PL3 and they still have no problems.
    Also a few threads above someone is using a PL3 and a PL4 together and only the PL4 has issues.
    I am new to GHL with the PL4 but if I understand the other posts correctly - the probe design has not changed and the PL3 seems to have no problems in reading a consistent cunductivity.
    My Probe is drifting more than 5 percent and I need a solution for that.
    Actually I can not trust the probe... I tried all possible locations in the sump. Next and final try is a housing for the sensor. If this is not working, I will borrow me a PL3 from a friend (who is also using the PL4 since yesterday- but for freshwater) and test my probe with the PL3....

  10. #20
    Join Date
    30.04.2017
    Location
    Regensburg
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    1

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    I have been measuring conductivty on my new P4 for 3 weeks with exactly the same problem. I have tried recalibration as described before but up to now no success. Has anyone found a solution to this?

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