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Thread: How often should probes be tested and are there issues that can trip them up.

  1. #1
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    How often should probes be tested and are there issues that can trip them up.

    So I set up the apex 2016 around June 15th.
    Calibrated probes and all that.

    Today as I was mixing a new batch of water I tested the water with a refractometer that I calibrated with solution.

    To my surprise, the salt ppt came in at nearly 5 below what the probe was giving me
    (Probe at time was 33.8, refractometer 28!)

    More amazing that corals & fish still are doing well.

    A little surprised it was off by that much and so soon. Are there things that can interfere with accuracy or degradation over time.


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  2. #2
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    Did you calibrate immediately or let the probe soak first?

    Have you calibrated since then?

    Did you set temp compensation and if so what to and was the temp probe reading the same temp as the solution?

    What temp was the solution when you calibrated?

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

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    Quote Originally Posted by zombie View Post
    Did you calibrate immediately or let the probe soak first?

    Have you calibrated since then?

    Did you set temp compensation and if so what to and was the temp probe reading the same temp as the solution?

    What temp was the solution when you calibrated?

    You might be an engineer if...You have no life and can prove it mathematically.
    Zombie-
    All of them are good questions. I thought I had calibrated first but I can't recall if I did any of those things.

    I have not calibrated since then as I need to get the calibration solutions. Reading the labels, they are for once use only or at least the ones Neptune sent. Should be getting the new ones tues or wed.





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    Quote Originally Posted by zombie View Post
    Did you calibrate immediately or let the probe soak first?

    Have you calibrated since then?

    Did you set temp compensation and if so what to and was the temp probe reading the same temp as the solution?

    What temp was the solution when you calibrated?

    You might be an engineer if...You have no life and can prove it mathematically.
    Reading some other threads. That is reduce temp to 77, keep solution in sump for 15-30 min, and then calibrate preferably within sump.


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    Quote Originally Posted by Faulker's Maze View Post
    Reading some other threads. That is reduce temp to 77, keep solution in sump for 15-30 min, and then calibrate preferably within sump.


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    Correct. Except the tank only needs to be 77 the first time so you don't have to calibrate again if you need to adjust temp compensation. Once temp compensation has been tuned (2.2 usually works for 35ppt tank, 2.1 for 33ppt tank) you can do any temperature as long as the temp probe and solution are the same temp.

    Another thing to keep in mind as well is that your freshly mixed NSW unless also heated to tank temp will read low by roughly 2.2 ppt per degree C.

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

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    Frequent Contributor zombie's Avatar
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    Just realised I never answered your thread title. Outside of redoing the conductivity to make sure it's right, these are the recommended calibration schedules. As the probes age you will need to stick to the low end of the range but can do less often when still relatively new if you wish.

    - pH: every 1-2 months
    - conductivity: every 3-4 months
    - ORP: once or never
    - Temp: yearly of you have access to NIST traceable thermometer.
    - DOS: every 1-2 months

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

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    Thanks for the info. Much appreciated.


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    Quote Originally Posted by zombie View Post
    Correct. Except the tank only needs to be 77 the first time so you don't have to calibrate again if you need to adjust temp compensation. Once temp compensation has been tuned (2.2 usually works for 35ppt tank, 2.1 for 33ppt tank) you can do any temperature as long as the temp probe and solution are the same temp.

    Another thing to keep in mind as well is that your freshly mixed NSW unless also heated to tank temp will read low by roughly 2.2 ppt per degree C.

    You might be an engineer if...You have no life and can prove it mathematically.
    If I have it set perfectly to 77 though do I need to do any temp compensation at all then.


    I am slowly lowering the temp to 77 over next couple days from 78. Can't hurt anyway as 78 seems to be top temp anyway for most part f my livestock.


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    Quote Originally Posted by Faulker's Maze View Post
    If I have it set perfectly to 77 though do I need to do any temp compensation at all then.


    I am slowly lowering the temp to 77 over next couple days from 78. Can't hurt anyway as 78 seems to be top temp anyway for most part f my livestock.


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    I still would use it as it will stabilize your calibrations and will flatten your conductivity graph so it doesn't respond to hysteresis from your heater (a typical hysteresis of 0.5 degree will vary conductivity by 0.6 ppt even though it never actually changed without temp compensation) but tuning becomes less important the closer you get to 77 as the error becomes unnoticeable and irrelevant. So you could get away with just setting 2.2 and it will be close enough near 77 degrees (an improper tune at 77.5 degrees is only an error of up to 0.05 ppt)

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

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    Quote Originally Posted by zombie View Post
    I still would use it as it will stabilize your calibrations and will flatten your conductivity graph so it doesn't respond to hysteresis from your heater (a typical hysteresis of 0.5 degree will vary conductivity by 0.6 ppt even though it never actually changed without temp compensation) but tuning becomes less important the closer you get to 77 as the error becomes unnoticeable and irrelevant. So you could get away with just setting 2.2 and it will be close enough near 77 degrees (an improper tune at 77.5 degrees is only an error of up to 0.05 ppt)

    You might be an engineer if...You have no life and can prove it mathematically.
    Duly noted! Thank you.


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