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Thread: Salinity probe doesn't match my reads

  1. #1
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    Salinity probe doesn't match my reads

    I'm using a refractometer to test my salinity, calibrated before use, and I am about 5 points off??im at 35 on the button, and its reading 40. I just got my controller tonight. I know the ORP is going take some time to acclimate to the tank, but I didn't see anything about the salinity probe needing this time. By the way, I set it up by the book. Using the calibration on the probes when called for.

    Looking for any help, thanks in advance.

  2. #2
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    I had the same problem when I bought my 2016 and still to this day 2 months later it's still wrong. Salinity was one of the reasons I went with the 2016.


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    Miracles in Glass Custom 170 (220G), Building a Obsession Custom Sump, Vectra L1, AI Hydra26's, Geo618, Masterflex pump, Apex

  3. #3
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    I'm having the same issue, my refractometer is reading 35 dead on. Over the last two days my apex says it has creeped from 40 all the way up to my current reading of 53.1. I also calibrated my probe before use. Also I put it in a cup of tank water outside of my tank to see if it might be picking up stray voltage, but it gave me the same reading.

  4. #4
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    Following..Same problem here...

  5. #5
    NSI Member Krazie4Acans's Avatar
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    Quote Originally Posted by Cmuncie View Post
    I'm having the same issue, my refractometer is reading 35 dead on. Over the last two days my apex says it has creeped from 40 all the way up to my current reading of 53.1. I also calibrated my probe before use. Also I put it in a cup of tank water outside of my tank to see if it might be picking up stray voltage, but it gave me the same reading.
    Did you let the probe run in the sump for a week before trying to calibrate it (it's not required but I get better calibrations when I do this)? Have you tried changing where the cable from the probe is routed to see if it's being affected by stray power noise?

  6. #6
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    Quote Originally Posted by Krazie4Acans View Post
    Did you let the probe run in the sump for a week before trying to calibrate it (it's not required but I get better calibrations when I do this)? Have you tried changing where the cable from the probe is routed to see if it's being affected by stray power noise?
    No, I have only had the Apex running for 6 days so far. I will try moving the cord and in a few days I will re calibrate. Thanks for the info!

  7. #7
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    I calibrated as the instructions required. So now I have to buy more fluid to recalibrate after running it for a week in my tank? Nice. Good to know 800$ gets you a really good controller with sub par probes.

    - - - Updated - - -

    I have moved the probe around and have made sure it clear of other cables. Again, after some in depth reading, it seems like a LOT of people are having issues. The systems been out a year. Surely they should have had this resolved by now.

  8. #8
    Frequent Contributor zombie's Avatar
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    Cables aren't the only thing you need to be worried about for EMI. There are three potential sources that all need to be checked if you're readings are off. This has nothing to do with neptunes design. It's inherent in the physics of the probe itself and there is nothing neptune can do to fix it. Even $1,000 laboratory grade probes have these issues.

    1. The BNC cable needs to be 1in or more from any current carrying cord.
    2. The probe needs to be placed away from any pumps. Anything less than 6in can affect readings
    3. There can't be stray voltage in the tank. Check this with a voltmeter with the black in the ground of an outlet and the red in the tank. Poor quality or failing pumps and heaters can cause this.



    Side note: all probes (conductivity included) need to be calibrated regularly to provide accurate readings. It's annoying that it's an extra recurring expense, but monthly calibrations are the common practice. You can always get 25 packs on eBay for a pretty good price.

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  9. #9
    Frequent Contributor zombie's Avatar
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    Also, did you calibrate your refractometer as well? It's possible your refractometer is reading high and the cond probe is reading low.

    Sent from my SM-G935V using Tapatalk

  10. #10
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    Quote Originally Posted by zombie View Post
    Also, did you calibrate your refractometer as well? It's possible your refractometer is reading high and the cond probe is reading low.

    Sent from my SM-G935V using Tapatalk
    Yes. I calibrated it as well. I'll look into the other issues tonight and see what I can do.

  11. #11
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    I'm having the same issue, my calibrated refractometer is saying 1.024 and the Apex probe is showing 39.5. I calibrated the apex probe per the instructions.

  12. #12
    Frequent Visitor Scott.h's Avatar
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    I went through this when my probe was new. It seems to like a little slime coating. Already mentioned, keep it well away from cords and pumps helped me a lot. Also make sure there are no bubbles from an overflow or skimmer getting inside. Lastly make sure to float the calibration solution and make sure the temp probe and calibration solution are the same. Mine stays really really close to my refractometer for a few months before drifting a bit. The calibration solution is less then 2 bucks so I just keep one on hand when I make an order. Really for me its just a safeguard for my ato

  13. #13
    Regular Vistor
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    How long are salinity probes supposed to last? I've had mine a year and just over a week ago, the CONDX4 reading spiked to 50! I was freaking out but, after checking with my refractometer, the salinity was fine.

  14. #14
    Frequent Contributor zombie's Avatar
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    Quick spikes mean bubbles or debris not a bad probe.

    A cond probe should last several years (I believe Russ is still using his cond probe from 2011 or 2012). You will know it is going bad when it consistently drifts to incorrect readings (like 0.5+) between calibration cycles if you calibrate every 2 or 3 months.

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

  15. #15
    Frequent Visitor Scott.h's Avatar
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    I thought this would be a good example to show something. I don't have anything electrical (pumps, powerheads, etc) around my probes because it causes interference, but I do have my wires neatly zip tied together as they make their way along the back of my sump. Last night I had to add a new wire to the mix and simply cut all the zip ties so the existing wires are hanging loosely. See the pic of my graph and what a difference this alone makes. For accurate readings it really is important to keep the probes and wires isolated.

    S.PNG

  16. #16
    Regular Vistor
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    Thanks! I'll try and clear it and see how that goes.

    Quote Originally Posted by zombie View Post
    Quick spikes mean bubbles or debris not a bad probe.

    A cond probe should last several years (I believe Russ is still using his cond probe from 2011 or 2012). You will know it is going bad when it consistently drifts to incorrect readings (like 0.5+) between calibration cycles if you calibrate every 2 or 3 months.

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

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