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Thread: Fluctuating conductivity??

  1. #1
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    Fluctuating conductivity??

    Okay so I know my salinity probe wasn’t calibrated correctly due to me not following the steps... i need to redue this when I get another packet. But my problem is my probe reads between 37.4 and 36.8 which is high but my calibrated refractometer reads 1.026.

    My question is... calibrated the right way or not... isn’t salinity not suppose to fluctuate the way it is for me? I thought maybe salt creep was getting into my ATO reservoir but I measured and it’s fine.

    Also while we are on the topics of probes... my ph probe is fluctuating between 7.7-7.9... isnt this on the lower side?


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    The reason for the fluctuation is temperature compensation. Either you didn't enable it (it should be enabled) or the value needs adjustment from the default of 2.2. With a perfectly calibrated probe and temp compensation tuned to the right value, you should expect a variation of +-0.2 ppt throughout the day with a typical heater hysteresis.

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

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    Are you referring to the salinity probe or the ph probe?


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    Quote Originally Posted by Sobo's Reef View Post
    Are you referring to the salinity probe or the ph probe?


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    The salinity probe.

    Your pH value if definately on the low side, but it may or may not be correct. If you use a calcium reactor, you have low aeration, you don't run a refugium, you run a FOWLR tank, etc could all explain a low pH and if you had a combination of the above it might actually be correct. The easiest way to know for sure is to recalibrate then test the pH probe in the packets again before placing in your tank.

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

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    Well I have good aeration throughout the tank, I have a refugium but the tank is still fairly new so I only have a few pieces of LR in there.. no chaeto or anything. I guess I’ll have to get the more packets and calibrate again to be sure.


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    Quote Originally Posted by Sobo's Reef View Post
    Okay so I know my salinity probe wasn’t calibrated correctly due to me not following the steps... i need to redue this when I get another packet. But my problem is my probe reads between 37.4 and 36.8 which is high but my calibrated refractometer reads 1.026.

    My question is... calibrated the right way or not... isn’t salinity not suppose to fluctuate the way it is for me? I thought maybe salt creep was getting into my ATO reservoir but I measured and it’s fine.

    Also while we are on the topics of probes... my ph probe is fluctuating between 7.7-7.9... isnt this on the lower side?


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    37.4 PPT converts to 1.0282 SG
    36.8 PPT converts to 1.0277 SG

    You are talking about a 1.0005 SG fluctuation. Your refractometer cannot measure down that far so you wouldn't notice this if all you are using is a refractometer.

    Other thing to remember is this is a constant read vs taking samples.


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    Quote Originally Posted by vhuang168 View Post
    37.4 PPT converts to 1.0282 SG
    36.8 PPT converts to 1.0277 SG

    You are talking about a 1.0005 SG fluctuation. Your refractometer cannot measure down that far so you wouldn't notice this if all you are using is a refractometer.

    Other thing to remember is this is a constant read vs taking samples.


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    That’s actually a very good point. Never thought of it like that. Thanks!


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    Quote Originally Posted by Sobo's Reef View Post
    That’s actually a very good point. Never thought of it like that. Thanks!


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    Yes, to a point, except that your conductivity isn't the part that's actually fluctuating. What is happening is that the probe reading is heavily skewed by temperature somewhere in the vicinity of 2.2ppt per degree Celcius. Temp compensation is meant to resolve this natural error due to temp, but the exact value is dependent on a lot of things from base conductivity value to the relative concentrations of Mg and KH compared to Cl. This can be tuned to a certain extent, but say for example the actual value for your tank was 2.25 and you tuned yours for 2.2. If you tank temp fluctuated between 77.5 and 78.5, conductivity would fluctuate a bare minimum of 0.2 ppt (0.1 for tolerance +-0.05 ppt and 0.1 for the error in temp compensation value). There is also some variation from ATO and some variation from the amount of microbubbles present near the probe. This is why a daily variation of 0.4 is well within reason and what your ideal target should be.

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

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    Alright cool.. thanks a lot guys. I’ll update as I re calibrate both probes


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