Urgent help needed Salinity Issue : What to trust???

Discussion in 'Urgent Help Needed' started by costa, 5 Jun 2011.

  1. costa

    costa

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    Hi guys,

    Perhaps you can help me with an issue that has only recently surfaced.

    I have had my tank for about 2 years now and there has never been any salinity
    issues.
    The refractometer I have been using has always been spot on and I checked its
    reading again last week using one of those big floating hygrometers....they both
    gave me the same reading.

    Today, however, I did a water change and decided to check the 2 meters again:
    Hygrometer 1.030 Refractometer 1.050 ( I have checked the calibration)

    ????????? My question is this: Which reading do I trust and why?? :(

    I would appreciate any advice on this issue? Cheers.
     
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  3. Evo R

    Evo R

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    Those plastic meters are known to be inaccurate. And if your calibration is correct then I suspect your refracto is at its end. Rather ask a member that lives close to test your water just incase!
     
  4. rakabos

    rakabos

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    Make sure the refracto is calibrated to 0 with RO or tapwater at tank temp, then re-test...
     
  5. viper357

    viper357 Admin MASA Contributor

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    How did you calibrate the refactometer?
     
  6. costa

    costa Thread Starter

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    Hi Viper,

    I used R.O. water as well as the water vial that came with the refractometer for
    calibration. They both indicated a 0.0 reading on the refractometer.

    Oh, the other hygrometer is made of glass and is about 30-40 cm in length, and is
    not of the plastic sort.
     
  7. Mekaeel

    Mekaeel Moderator MASA Contributor

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    Personally, I will trust a well calibrated Refractrometer any day over the floating hydrometers. And I agree with Evo's point, it could bee stuffed. Did you perhaps drop it or did it get damaged?
     
  8. costa

    costa Thread Starter

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    Thanks Mek!

    I also prefer the refractometer. I will have it checked out...hopefully the floating
    hygro is at fault.

    The refractometer is stored away safely so I'm baffled at the moment. Will take a
    sample of the water to my LFS.
     
  9. B2048

    B2048

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    Could it be temperature related? Does your refractometer do ATC?
     
  10. robvdv

    robvdv

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    I have a similar problem. I use a swing-arm (don't laugh) and it's worked fine for me for 10 years. Before that I used a hygrometer. Anyway, I've recently started to become suspicious of the swing-arm, so I tested 350g salt mix dissolved in 10kg of water (not exactly scientifically correct, I know) and was a bit shocked. The swing-arm showed 1.020. It should have shown 1.026, or 35ppt. Unfortunately I don't have any NSW handy to triple check.

    Anyway, I think it's time to grow up and get a refractometer.
     
  11. costa

    costa Thread Starter

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    Interesting fact that B2048. The refractometer I have is the W 211/ATC, so yes
    I presume it does. Which begs the question, is that why the floating hygrometer is about
    0.03 lower?
     
  12. Reef Maniac

    Reef Maniac MASA Contributor

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    Guys, if I may nit-pick, the floating instrument used to measure the SG of a liquid is called a hydrometer, and not a hygrometer...

    All hydrometers are calibrated at a specific temperature, and would give false readings at any other temperature, as the density of any liquid varies with it's temperature. Having said that, most (reputable) marine hobby type hydrometers are calibrated for 25°C, and the difference in SG between that and (say) 24°C or 26°C is negligible.

    costa, have you been floating your glass hydrometer in your tank or sump for any length of time (i.e. do you leave it in your tank between readings). If so, perhaps it just needs a decent clean up, as it could have become covered in calcium deposit and/or algae (either of which would affect it's "floatability", and thus it's accuracy. Touching the instrument with fatty/oily hands could have the same effect.

    If you have fish and corals in that tank, and if they look healthy and normal, I would suspect that the refractometer is wrong, as such a high SG would be quite bad for the livestock.

    Hennie
     
  13. Nemos Janitor

    Nemos Janitor

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    Hmm.... the diference between 1,030 and 1,050 is huge and i would quary and say the readings and information supplied is incorrect.

    However if the readings were 1,023 and 1,025 i would say this is normal as hydrometers are calibrated at sea level and at temprature and read about 0,002 lower in gauteng.
     
    Last edited: 6 Jun 2011
  14. Mad_Max

    Mad_Max

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    Use distilled water to calibrate as per user guide. You can get it from a chemist.
     
  15. Nemos Janitor

    Nemos Janitor

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    Last edited: 6 Jun 2011
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