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Thread: Conductivity Conversions

  1. #1
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    Conductivity Conversions

    I am using the conductivity probe on my apex and the current measurement is 43.3

    I separately measured the salinity of my water to see if the conductivity probe was accurate and it read 1.026.

    Is there a way for my apex to show the 1.026 reading instead of the 43.3? How do i convert the 43.3 to 1.026? Does 43.3 equal 1.026? Is there some kind of conversion chart?

    I am also using the i phone app and cant figure out how to show the measurement as 1.026?

    Any help would be appreciated!
    Thanks
    Mike

  2. #2
    Master Control Freak aquamanic's Avatar
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    Conductivity which is what this probe measures, is represented in parts per thousand (PPT)

    Specific gravity which is what you're referring to is measured with a hydrometer. There are plenty of conversion tables available on the Internet to go from one to the other.

    Remember though that all conversions are rough. They're two different measurements.

    Here's one such conversion
    http://www.hamzasreef.com/Contents/C...Conversion.php

    You'll probably find different results with different calculators though.
    Al

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  3. #3
    Master Control Freak RussM's Avatar
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    Conductivity Conversions

    Which scale is the probe set for in the Apex? Conductivity or Salinity? 43.3 isn't a normal reading. For conductivity, a normal reading is about 53 mS; normal for salinity is about 35 ppt
    Please do not send me PMs with technical questions or requesting assistance - use the forums for Apex help. PM me ONLY if the matter is of a private or personal nature. Thanks.

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    it is set for salinity. maybe I should re-calibrate the probe?

  5. #5
    Frequent Contributor zombie's Avatar
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    I would recalibrate. Also, if your probe hasnt soaked for a week in your sump, the readings will be garbage.

  6. #6
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    Well, I did calibrate my probe and the APEX displays 33 (ppt) while my refractometer reads 36.
    How accurate is the APEX salinity probe. Does it require the temperature probe for temp. compensation or will the probe on the base unit be enough?

    BTW: does anybody know what the cell constant of the APEX salinity probe is and if you could also use other probes?

  7. #7
    Frequent Contributor zombie's Avatar
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    Temp compensation will only work with a probe plugged into the PM2. Its pretty accurate with temp compensation and a good calibration routine (ie float the calibration solution in your sump for 15 minutes before calibrating. Let the probe settle for 5 minutes in the solution while floating in the sump). If you use that routine and the value is still low, adjust the temp compensation value until it is close to the refractometer reading (most people use 2.2 for temp compensation).

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    So my CONDX3 reads 36.5 (35 = 1.026) I then measured it with my Milwaukee MA887, and it reads 1.026.
    What's going on?

    My APEX 4 days old, I calibrated it, is was reading 1.026 4 days ago.
    My MA887, is new, less than a week old.
    I even read 1.026 on my hydrometer.

    I did change some water.

  9. #9
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    Quote Originally Posted by Turok View Post
    So my CONDX3 reads 36.5 (35 = 1.026)My APEX 4 days old, I calibrated it, is was reading 1.026 4 days ago.
    I don't have a PM2 but from what I have read on here you should let it soak in the sump for about a week and then calibrate the probe or you are going to get a whole bunch a inconsistent readings...
    Jon

  10. #10
    Frequent Contributor zombie's Avatar
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    ^this

  11. #11
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    There is nothing to soak on a conductivity cell. In essence it's just two platinum electrodes, either in plate or in ring form. The only thing that "soaking" might do is let a bacteria film grow on the electrodes, which of course will alter the conductivity reading.
    The basic issue is that this type of conductivity probe is designed for lab use, meaning it being in the test sample for a few minutes and then cleaned and dried for the next test. Prolonged immersion will sooner or later cause false readings. To achieve high accuracy you would need to clean it daily or at least weekly and then check the calibration and recalibrate as needed. The longest any of the probes (pH, ORP, Conductivity) should go without cleaning and checking of calibration and if needed recalibration is one month.

    Another, more serious issue I have with the APEX conductivity probe is that it collects air bubbles that have to be shaken out several times a day or the probe will have a lower reading.

    The issue with the calibration not being right, especially if too high, might go back to the same air bubble issue: if you calibrate the probe with some bubbles in it you might get a higher reading if you don't have bubbles (or just less) during the measurement. So you need to tap the probe against the container (I use a PET bottle pre-form) with the calibration solution to dislodge and expel all bubbles that may be trapped inside the probe and then wait a minute before hitting the "done" button.
    Last edited by ThRoewer; 03-11-2015 at 11:36. Reason: clarification

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    My new unit is reading 36.5 ppt, and using the conversation calculator here that comes out to about 1.0275.

    However, using my calibrated Milwaukee digital refractometer, my tank is at 1.026.

    Is there a way to manually adjust the conductivity probe to match my refractometer?

    Also, can you force the Apex to show salinity instead of conductivity in ppm? My brain convert ppt all that easily after using salinity for so many years...

  13. #13
    Frequent Contributor zombie's Avatar
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    Quote Originally Posted by deputydog95 View Post
    My new unit is reading 36.5 ppt, and using the conversation calculator here that comes out to about 1.0275.

    However, using my calibrated Milwaukee digital refractometer, my tank is at 1.026.

    Is there a way to manually adjust the conductivity probe to match my refractometer?

    Also, can you force the Apex to show salinity instead of conductivity in ppm? My brain convert ppt all that easily after using salinity for so many years...
    Just because your Milwaukee says 1.026 does not mean 36.5 is inaccurate. That Milwaukee even when properly calibrated has an error of 0.001 SG and the conversion from ppt to SG can also vary 0.001 SG depending on the type of salt you use.

    I would change the reading on your Milwaukee to ppt because that is what it is actually measuring. Just like metric vs imperial, ppt is a vastly better unit to use because it makes any calculations a million times easier.

    Sent from my SM-G965U using Tapatalk

  14. #14
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    Quote Originally Posted by zombie View Post
    Just because your Milwaukee says 1.026 does not mean 36.5 is inaccurate. That Milwaukee even when properly calibrated has an error of 0.001 SG and the conversion from ppt to SG can also vary 0.001 SG depending on the type of salt you use.

    I would change the reading on your Milwaukee to ppt because that is what it is actually measuring. Just like metric vs imperial, ppt is a vastly better unit to use because it makes any calculations a million times easier.

    Sent from my SM-G965U using Tapatalk
    That sounds like good advice. Thank you.

    If the ideal salinity reading is 1.026 in a reef tank, what is the comparable ideal PPT reading I should be shooting for so I know what to look for on my Milwaukee unit.

  15. #15
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    Using RHF reference, it looks like 35ppt is the target number. Or thereabouts.

    http://reefkeeping.com/issues/2004-05/rhf/

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    Quote Originally Posted by zombie View Post
    Just because your Milwaukee says 1.026 does not mean 36.5 is inaccurate. That Milwaukee even when properly calibrated has an error of 0.001 SG and the conversion from ppt to SG can also vary 0.001 SG depending on the type of salt you use.

    I would change the reading on your Milwaukee to ppt because that is what it is actually measuring. Just like metric vs imperial, ppt is a vastly better unit to use because it makes any calculations a million times easier.

    Sent from my SM-G965U using Tapatalk
    So I took your advice, as always

    I zero'd the Milwaukee out with distilled water and switched it to read PPT.

    It's currently reading 35ppt, which is perfect.

    However, my Apex is reading 36.7.

    Can I force calibrate the Apex to read like my Milwaukee unit? I'm guessing the Milwaukee unit is more accurate than the Apex probe.

  17. #17
    Just a Nerd in the Herd alb's Avatar
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    If it's the same Milwaukee that I've got, it's +/- 2 PSU.

  18. #18
    Frequent Contributor zombie's Avatar
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    Quote Originally Posted by deputydog95 View Post
    So I took your advice, as always

    I zero'd the Milwaukee out with distilled water and switched it to read PPT.

    It's currently reading 35ppt, which is perfect.

    However, my Apex is reading 36.7.

    Can I force calibrate the Apex to read like my Milwaukee unit? I'm guessing the Milwaukee unit is more accurate than the Apex probe.
    Since you calibrated with distilled water and not 35 ppt calibration fluid, it's still possible the apex is right and the Milwaukee is off. Until you check the Milwaukee against a 35ppt refractive calibration solution (you can make this at home with table salt if you have an accurate scale) I would not make any assumptions about which is the right value.

    Sent from my SM-G965U using Tapatalk

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    Quote Originally Posted by alb View Post
    If it's the same Milwaukee that I've got, it's +/- 2 PSU.
    What is PSU? I have only been working with SG up to this point and now, PPT.

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    Quote Originally Posted by zombie View Post
    Since you calibrated with distilled water and not 35 ppt calibration fluid, it's still possible the apex is right and the Milwaukee is off. Until you check the Milwaukee against a 35ppt refractive calibration solution (you can make this at home with table salt if you have an accurate scale) I would not make any assumptions about which is the right value.

    Sent from my SM-G965U using Tapatalk
    Fair enough. You can't calibrate to a certain number with the milwaukee, just zero it out with distilled water per their directions. That being said, the most I've ever seen it deviate during a recalibration is .001

    My Apex probe all of a sudden went form 36ish to 43ppt. Not sure what that's about.

    Any idea where I can get a bunch of 35ppt and probe calibration packs? Might as well buy a half dozen of each as it looks like I'll be doing this semi regularly.

  21. #21
    Master Control Freak RussM's Avatar
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    Quote Originally Posted by deputydog95 View Post
    What is PSU? I have only been working with SG up to this point and now, PPT.
    “PSU is an acronym for practical salinity units, which is essentially a modern replacement for ppt, since salinity is no longer defined as directly relating to solids in the water, but rather by its conductivity.”

    (Taken from this article: http://www.reefkeeping.com/issues/2004-06/rhf/index.php)
    Please do not send me PMs with technical questions or requesting assistance - use the forums for Apex help. PM me ONLY if the matter is of a private or personal nature. Thanks.

  22. #22
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    Quote Originally Posted by RussM View Post
    “PSU is an acronym for practical salinity units, which is essentially a modern replacement for ppt, since salinity is no longer defined as directly relating to solids in the water, but rather by its conductivity.”

    (Taken from this article: http://www.reefkeeping.com/issues/2004-06/rhf/index.php)
    Interesting. Thanks for the link.

    I would assume since the Apex displays in PPT, it makes the most sense to work off PPT numbers, right?

  23. #23
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    Quote Originally Posted by deputydog95 View Post
    My Apex probe all of a sudden went form 36ish to 43ppt. Not sure what that's about.

    Any idea where I can get a bunch of 35ppt and probe calibration packs? Might as well buy a half dozen of each as it looks like I'll be doing this semi regularly.
    If your probe was calibrated immediately after opening and didn't soak in your sump for a few days first, the drift is normal though a little higher change than normal. Your procedure for calibration needs to be very precise for accurate calibration and you must rinse in RO and lightly pad dry for the dry step, the calibration packet must exactly match tank temp, and there can be no bubbles in the probe when doing the wet step. If any of those steps are not perfect, the probe won't be accurate

    I bought a bunch off amazon and now I just make my own with table salt since I have a scale with a very high precision (6 significant figures).

    Sent from my SM-G965U using Tapatalk

  24. #24
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    Quote Originally Posted by zombie View Post
    If your probe was calibrated immediately after opening and didn't soak in your sump for a few days first, the drift is normal though a little higher change than normal. Your procedure for calibration needs to be very precise for accurate calibration and you must rinse in RO and lightly pad dry for the dry step, the calibration packet must exactly match tank temp, and there can be no bubbles in the probe when doing the wet step. If any of those steps are not perfect, the probe won't be accurate

    I bought a bunch off amazon and now I just make my own with table salt since I have a scale with a very high precision (6 significant figures).

    Sent from my SM-G965U using Tapatalk
    Ok, I'll get some 35ppt fluid and whatever the apex fluid uses for the probe and see what I can do to get it all lined up.

    The weird thing was, after I calibrated it (half assed), it was kind of close. When I added the temp correction, it got really close but I didn't recalibrate. Then it went sideways

    I'll get more fluid and start over again.

    I actually run all my probes in the display tank. I know some people don't like the look, but I prefer to measure right where the animals are. My heaters are in the DT tank too. So when I pause the pumps for say a feeding for 30 mins or so, the temp remains constant despite the AC blowing hard in our office.

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    Does this look like the appropriate solution to validate how close my Milwaukee is to being accurate?

    https://www.amazon.com/FTCo-Refracto.../dp/B00OHYRB02

    I can't find the Apex calibration solution for the cond. probe on amazon, but most of the larger reef sites have plenty in stock.

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