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Thread: pH probe reading low ???

  1. #26
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    Another update. Just cross-checked against a new hand-held pH meter (Dr Meter, pH 100) calibrated at 6.86, and it's basically spot on. Apex reads 7.77, Dr Meter 7.8. Apex reads the calibration buffer as 6.86. I guess I have to take it all back ;-)

  2. #27
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    I don't have a meter to check, but I did order another probe. It's only 7$ and from China so we will see how that works out,


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  3. #28
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    Just an update. Purchased another pH probe (BRS one) and hooked it to the Apex. pH readings now match across all my devices.

  4. #29
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    Got probe for 7$. China. Don't do it.


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  5. #30
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    After reading the entire thread, i am sure something is not right with Apex, since i also get the same reading of about 7.72 at night and 7.78-7.80 in the afternoon, further upon checking with API and sali test kits, my ph always come 8.20 to 8.40. I have though calibrated the probe just once, dont know what to do, i am thinking to calibrate the probe once again. I think that the placement of probe also matters, since i have placed all my probes directly into the tank near the return just to get accurate reading from the tank itself. Any suggestions on how to go about it

  6. #31
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    I have had similar experiences. I am running two lab grade probes on apex. (Brs and neptune). Multiple calibrations with pinpoint solutions. And they run about .3 below seneye. Tried moving to different locations in tank with no affect in difference. This is over multiple seneye slides. I have not checked into calibrating seneye or adjusting it.

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  7. #32
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    I am using apex classic (gold)

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  8. #33
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    My probe has been reading the same a well. .3 exactly my Apex (brand new) shows 7.8 and my Seneye (brand new) shows 8.1. Has anyone been told that there is an issue with the probe? I have been running my system for almost 2 months now and would like some clarity.

  9. #34
    Apex User zombie's Avatar
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    Calibrate your probe again and make sure to let the value settle (I wait 5 minutes) and make sure there are no bubbles in the probe during the process. After calibration is complete verify that the probe reads 7.0 and 10.0 in each solution. If it doesn't recalibrate with the same solution. If it does, the apex value will be within 0.02 of the actual lab measured pH at any point between 7 and 10.

    If that reading after proper calibration doesn't jive with another test kit, Seneye, etc. Check that the apex probe reading is the same in the tank compared to a cup of tank water isolated from the tank. If that reading is identical, you can be certain the apex is right and the secondary measurement is wrong. If the reading changes, you have an electrical interference or stray voltage issue that must be found and eliminated.

    You might be an engineer if...You have no life and can prove it mathematically.

  10. #35
    NSI Member Krazie4Acans's Avatar
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    The temp of the calibration solutions should also match the tank temp and be maintained during the calibration. Then once calibrated you can turn on temperature compensation which will help reduce reading swings due to temperature changes in the tank.

  11. #36
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    Thank you Zombie- Thank you Krazie4Acans. I received an email from Apex and they instructed me to do the similar steps you guys suggested. I am a new user and used the auto calibration. I was instructed to use the manual calibration which I think is way more precise. I really let the probes sit for a bit. All is right with the world my PH bounces between 8.12 and 8.29 so I am very happy. now will re calibrate in 6 months.

  12. #37
    NSI Member Krazie4Acans's Avatar
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    That's great to hear.

  13. #38
    Apex User zombie's Avatar
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    Quote Originally Posted by Krazie4Acans View Post
    The temp of the calibration solutions should also match the tank temp and be maintained during the calibration. Then once calibrated you can turn on temperature compensation which will help reduce reading swings due to temperature changes in the tank.
    While this is terribly important for conductivity, the effect is nearly neglegable for pH because the calibration solutions are temperature buffered and pH probes are not highly temperature dependent. In even extreme cases the error is likely to be less than 0.05. With that said, if you are determined to have absolute pin-point accuracy then the solution should match tank temp. Personally I don't bother with this step as I value my time more than 0.05 pH error.

    You might be an engineer if...You have no life and can prove it mathematically.

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