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Thread: Conductivity drops correlated to UV Sterilizer

  1. #1
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    Conductivity drops correlated to UV Sterilizer

    I have an Apex Gold running my 265 gallon salt water aquarium. I have noticed a correlation between odd Conductivity readings with a recently installed UV sterilizer being on. With the UV off, the conductivity reads 45.8. When it turns on, the conductivity drops to around 23.2.

    Apex Fusion Conductivity.jpg

  2. #2
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    Forgive me, but why is your UV cycling on and off? I never seen it done other than constant on.
    When it does turn on, are you activating flow with it, or is flow constant?
    It seems you could have stray voltage or microbubbles hitting the probe at that time? From a pump or the UV?


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  3. #3
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    Constant flow & all return from the pump goes through the UV - the cycling is only turning the UV lights power on & off. The UV Sterilizer is oversized for my tank & flow rate.

    Probe is located in the refugium & there is no perceivable change in bubbles or flow in the refugium & no other powered device cycling during that time.

    I've also rerouted the cables for the UV power, Apex cables, & probe cables/placement to minimize induced voltages.

  4. #4
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    I have this very same issue. My conductivity shows 30.8 when my 50W enormous UV Sterilizer is turned on, and it jumps to 32.5 when I turn it off. My two redundant refractometers read around 33, but the moment on turn on my sterilizer, the reading dips down to 30.8.

    What gives? Turning off other components doesn't effect the conductivity reading. Why would turning on/off a lightbulb a big difference?

  5. #5
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    Do you have a grounding probe in your tank?

  6. #6
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    Quote Originally Posted by jonlovisolo View Post
    Do you have a grounding probe in your tank?
    I don't have one anymore after using one in a previous tank tripped a GFCI outlet right as I was leaving for a weekend trip. Bad result.

    I've always thought grounding probes were of mixed reputation. Do you think they are worthwhile? Does conductivity get wonky when stray voltage is in the tank?

  7. #7
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    I won't argue the pros or cons of using a grounding probe, but I will say I'm an electrical engineer and I use several on my 120g tank.

    There's no question on the correlation between your conductivity probe and UV sterilizer, right?

    The conductivity probe consists of a set of platinum electrodes with a known size gap between them. The electrodes are excited with a precise voltage, and the resultant is measured. The conductivity of the water between the two electrodes determines the output reading, and our conductivity number is provided. This is fundamentally why a conductivity probe measures differently than a refractometer.

    But the signal is very small, and subject to interference. This is why it's critical to route your cables appropriately, as you have already done. If your cables are routed correctly, the only other way to interfere with the signal is to change the electrical characteristics of the water you're measuring.

    When you read the instructions on how to measure stray voltage, using a multimeter between tank water and ground, you're measuring the same stuff the conductivity probe is exposed to. If it's small, your conductivity probe will overcome it. If it's large, it's going to affect your reading. And turn tangs into living capacitors, which I believe is why some people report tangs are sensitive to stray voltage.

    Just curious, after the GFCI tripped, did you fix any equipment? GFCI's trip when electricity leaks out of a device and into our tanks. It's possible your UV sterilizer tripped your GFCI initially, and now, is honking with your conductivity measurement. GFCI's tend to be a bit sensitive, over time, but are usually a good indicator something has gone wrong.

    Sorry for the long winded response.

  8. #8
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    Quote Originally Posted by jonlovisolo View Post
    Sorry for the long winded response.
    Thank you for the very thoughtful response!

    The old tank didn't have the UV. I plugged in the probe to my power strip, dropped it in the sump, and the GFCI tripped. I was trying to catch a train so I reset the GFCI, it didn't trip again, and walked out. Some time in the next three days, it tripped and I lost everything, save for one clownfish who somehow held his breath for 3 days. It was my first massive loss, and I decided I would rebuild with a new stand (to make better plumbing) new tank, and better equipment. I spent a lot on a Trigger sump, Ecotech pumps, APEX 2016 system and an oversized UV sterilizer. The tank contents were transferred so I didn't have to re-cycle everything.

    Back to the new setup, I can switch my UV on and off (via APEX) and my conductivity reading goes up from 30.8 to 32.6. It takes about 1-2 minutes for the reading to change. I haven't gotten in there with a multimeter to check how much is being leaked, and I have not plugged in the grounding probe since that is still something I associate with my tank collapse.

    Since I'll be around the whole week, I'll give the grounding probe another chance and see how it affects the reading. I've been pulling my hair out trying to get a good salinity reading. I have two refractometers, and I calibrate one from 0 (RO/DI water) and another calibrated from 35 (solution) and they are off from one another by as much as 3 points, which is a big swing. My guess is that it is more accurate to calibrate from 35 than "all the way up" from 0. Thanks again for the help; I really appreciate your thoughtful response.

  9. #9
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    So, I plugged in the titanium probe tonight, and got zilch. It isn't on the same APEX Power Bar as my UV light, but that shouldn't make a difference for stray voltage. I have a Klein MM400 multimeter arriving tomorrow which should provide more info on what's happening in the tank.

    Here are two images from my APEX interface, showing the up/down that occurs with conductivity (labeled "salt") when I have the UV sterilizer outlet on (30.3) and then when I turn that UV sterilizer outlet off (jumps and settles at 32.6).

    Of note, when I use my 35-calibrated refractometer to test the water, it shows 30.5 or 31. That completely baffles me, as I would expect that turning ON a device would cause a change from the measured norm, not turning OFF a device creating a reading that is significantly different from reality. Thoughts, conspiracy theories?




    IMG_5830.PNGIMG_5831.PNG

  10. #10
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    I wonder if a ferrite bead around the probe wire would help in this case.

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  11. #11
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    I thought I had it figured out for a second. The salinity always jumps 2.3 units (ex. 32 to 34.3) when I turn the UV light off. The temperature compensation is set at 2.2 on the Salinity/Conductivity probe, so I thought setting that to zero would help.

    Nope!

    I've played around with that setting so much that I don't even remember if it's supposed to be at 2.2 or 0. I have pH, ORP, Conductivity, and Temp probes all hooked up to a 2016 Apex.

  12. #12
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    I'm having THE SAME issue!!! Have you guys resolved yours?

  13. #13
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    FIXED with grounding probe!

  14. #14
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    So you need to check which pump or item is putting stray current in your water, I would imagine...

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