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Thread: Salt ppt reading off?

  1. #1
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    Salt ppt reading off?

    We have had our Apex in service for since July 6 and I'm concerned about the salt reading. When we first put the probe in, it read 33.75 which was the same as our refractor. Since it's been in, the salt reading just keeps going up and now reads 55.1. I checked it with the refractor again and our salinity is 1.025 which should be about 34. I then recalibrate the refractor and checked again with the same result. Anyone know why this is happening?

  2. #2
    Frequent Contributor zombie's Avatar
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    Could be a few things.

    Probe could be dirty (soak in vinegar for 30 mins, lightly brush with a soft bristle toothbrush and rinse in water).

    You could also have a piece of equipment that the insulation is failing and/or the seal is broken. You can track this down using either a multimeter between the tank and ground or the conductivity probe itself. Start turning off devices one at a time until you see a noticeable change in conductivity/stray voltage. If you see something spike, that piece of equipment is going to start leeching copper soon if you don't replace it now.

    You could be getting electrical interference on the probe cable. Make sure the wire is at least 2" away from any other wires for as much of the length as possible.

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

  3. #3
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    First, just to rule out the obvious, make sure the probe is in fact reading salinity and not high range conductivity. I run mine in conductivity and the normal value there is 53.0, so you are right there.

    As that has been ruled out, verify you don't have interference. Move the probe around, check for entrapped air bubbles and gently work those out and then make sure the wires are straight but not parallel to electrical chords.

    Once you have checked all that, check the calibration on the probe. Get a bag of 53.0 uS/cm solution and see what it reads. If it does not read 53.0, re-calibrate the probe.

    Since you have reported a slow creep over time, my first bet will be micro air bubbles are collecting in the probe tip and building up over time.

  4. #4
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    i had to skew my calibration fluid to be able to offset the reading enough to be accurate. I used 53ms fluid and had to add some tank water to it to lower its salinity. Meaning...


    I calibrated like we should with 53ms fluid, then placed probed back into my sump and it would read like 29.5(give or take), or 1.0222. Problem is i know that my tank is at 33, or 1.0249 with a calibrated refractometer. I then tried to offset the temp correction and still couldnt get it close.


    So after a few trial calibrations I was able to get my probe to read what the actual tank is. I had to skew the calibration fluid, this took me three tries to get right or close enough to be able to adjust from there. So on the third try I was able to calibrate the probe with skewd fluid, then place the probe into my sump and got a reading of 32.7.


    From there, i was able to compensation via the apex to bring my probe to where the tank actually is, 33, or 1.0249.




    Most people say they only use the probe to track differences in salinity and not the actual salinity. Which is actually all i use mine for, BUT, now mine is reading correctly from the start, and now i can track a shift in salinity.

  5. #5
    NSI Member Krazie4Acans's Avatar
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    Modifying the calibration fluid results in a non-calibrated probe. If you change the one known, and factory calibrated item in this procedure then you have invalidated the calibration regardless of what reading you achieve. Be very careful in what actions you have your apex take based on this non-calibrated probe in your tank. You would actually be better off having a calibrated number that is way off than a non-calibrated number that is right on.

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    Quote Originally Posted by Krazie4Acans View Post
    Modifying the calibration fluid results in a non-calibrated probe. If you change the one known, and factory calibrated item in this procedure then you have invalidated the calibration regardless of what reading you achieve. Be very careful in what actions you have your apex take based on this non-calibrated probe in your tank. You would actually be better off having a calibrated number that is way off than a non-calibrated number that is right on.
    Fortunately enough I use no salinity programming. Only for visual check. So far mine has been dead on for over a month so far; cross checked with a calibrated refractometer.

  7. #7
    NSI Member Krazie4Acans's Avatar
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    How are you calibrating your refractometer? Using the same modified calibration solution used for the probe?

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    Quote Originally Posted by Krazie4Acans View Post
    How are you calibrating your refractometer? Using the same modified calibration solution used for the probe?
    Lol No, I would not use that.

    I use 35ppt calibration fluid from BRS.

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