Refractometer help needed

Discussion in 'Water Parameters and Additives' started by Greg Bridger, 16 Oct 2012.

  1. Greg Bridger

    Greg Bridger

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    I've just purchased a Refractometer and need a bit of advice. The instructions say the unit must be calibrated at 20 deg cel which I did now for the dilemma. Red Sea recommend a salinity of 33ppt at 25 deg but if my room temperature is 20 deg then this means that my salinity will change to about 31ppt when it comes into contact with the Refractometer that is at 20 deg. Any help will be great
     
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  3. Nemos Janitor

    Nemos Janitor

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    Is the refractometer an ATC refractometer?
     
  4. Greg Bridger

    Greg Bridger Thread Starter

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    Yup it is
     
  5. Nemos Janitor

    Nemos Janitor

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    First off temperature has no relevant effect on salinity so a salinity of 33 at 15c is the same as a salinity of 33 at 35c

    To achieve a salinity of 33 with your 20/20 ATC refractometer calibrated correctly, you need to get a SG of 1.0245 @ 20c
     
  6. Nemos Janitor

    Nemos Janitor

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    Maybe I jumped the gun a little here.

    On a ATC refractometer it is the temperature that the calibration is done that is important. It must be 20c on a 20/20 instrument. The instrument will compensate to instrument temperature change up to about 30c

    The sample water temp will not make a difference as it will quickly equilibrate to the instrument temperature.

    Most salt mixes refer to Hydrometer specific gravity (SG) which refers to a temperature of (normally 25c).
     
  7. Greg Bridger

    Greg Bridger Thread Starter

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    So what you are saying is as long as the calibration is done at 20 deg then the Refractometer will compensate for the difference between the aquarium temp and the Refractometer's temp
     
  8. Albert Terego

    Albert Terego

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    Yes that is correct. With an ATC Refractometer as long as you are reasonably close to room temp it'll be fine. Temperature does not have much of an effect on refractive index.
     
  9. Nemos Janitor

    Nemos Janitor

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    yes :thumbup:

    Remember that...

    The SG reading will be to a 20c referance.
     
  10. Greg Bridger

    Greg Bridger Thread Starter

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    Thanks for clearing up this guys
     
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