Refractometer vs Hydrometer

Discussion in 'Test Kits, Controllers, Reactors and Dosers' started by TaahirS, 9 Nov 2014.

Voter count: 53
?

Hydrometer or Refractometer

  1. Refractometer

    66.0%
  2. Hydrometer

    28.3%
  3. Refractometer because I don't know what a hydrometer is.

    3.8%
  4. Refractometer because I don't know how to use a hydrometer

    1.9%
  1. TaahirS

    TaahirS MASA Contributor

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    This topic has come up a few times and for interests sake would like to see if more people use hydrometers or refractometers to test for salinity.

    Vote on the poll
     
    Last edited: 9 Nov 2014
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  3. Ridwaan

    Ridwaan

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    I use the Tropic Marin hydrometer to check specific gravity...
    One of the best investments i made for my tank
     
    Last edited: 10 Nov 2014
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  4. Nemos Janitor

    Nemos Janitor

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    Yeah, the Tropic Marin hydrometer measures Specific Gravity not salinity.
     
  5. Nemos Janitor

    Nemos Janitor

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    This is an interesting one and I can guarantee at least 90% of those that polled have no clue into what their instrument is reading. It is not reading SALINITY. Most likely a specific graverty calculation. Salinity is a measurement of a percentage of the weight of irons (salts) in a weight of water. Normally expressed as a number. Typically marine water is S=35 or salinity = 35ppt. This is a weight to weight ratio and temperature has no influence.

    Specific gravity is a weight to volume ratio and temperature affects volume as does gravity and atmospheric pressure.

    The majority or hydrometers measure Specific Gravity. So they are tempurture dependent.

    All refractometers measure light refraction. This refraction of light is then calibrated to Specific Gravity on most instruments. Some have a Salinity scale.

    However refractometers are not accurate as refraction of light is tempreture dependent.



    SALINITY IS NOT temperture dependent and will not change with temperature fluctuations. A hydrometer cannot measure salinity without a salinity scale and tempurture compensation. The same for a Refractometer.

    SPECIFIC GRAVITY is temperture dependent and will change with temperture fluctuations.

    Polls of this nature highlight the number of reefers that have no clue what Salinity is. This is very disturbing as it is the primary parameter that any reefer needs to understand.
     
    Last edited: 10 Nov 2014
  6. carlosdeandrade

    carlosdeandrade

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    Use a conversion calculator. If you keep your tank at 25'C, you will always get the best readings as most scientific equipment is calibrated at this temperature.
    Here is a great calculator for all. I use it all the time.
    Salinity Conversion Calculator
     
    Last edited: 10 Nov 2014
  7. Vetrix

    Vetrix

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    Some refractometers have ATC, so they have temperature compensation.
    There is a lot of misunderstanding concerning the way the ATC feature works and its effect on the refractometer at different ambient room temperatures.
    Salinity is a measurement of a mass of salt in a mass of water and therefore does not vary with temperature however a refractometer does not measure salinity directly but measures the refractive index which is then displayed as salinity. The refractive index of a solution does vary with temperature therefore the reading that you measure with a refractometer is always temperature dependant.
    An ATC refractometer has a bimetal strip inside the instrument that moves the reading scale as the temperature changes to compensate for the change in refractive index.
    What people do not generally understand is that it is the temperature of the instrument and not the water temperature that is important as the small sample of water used for testing will equilibrate within seconds to the temperature of the refractometer.
    Once correctly calibrated at the set calibration temperature of 20oC the refractometer can then be used in environments where the ambient temperature and therefore instrument temperature would heat up or cool down within the range of the ATC which is between 10 and 30 centigrade.
     
  8. carlosdeandrade

    carlosdeandrade

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    Also, they are so sensitive to knocks and bumps. I will never go back to a refractometer. They have their place, but for a clumsy oaf like me, they just don't work. :D
     
    Last edited: 10 Nov 2014
  9. carlosdeandrade

    carlosdeandrade

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    That is why it is best to always immerse the tip of the refractometer in our aquarium water for ten minutes so that you can get the temp up on the instrument, especially in winter. Jsut remeber not to SOAK the whole refractometer.
     
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  10. TaahirS

    TaahirS Thread Starter MASA Contributor

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  11. reef addict

    reef addict

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    i prefer refractometer however also use a swing arm from time to time
     
  12. carlosdeandrade

    carlosdeandrade

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    As long as you calibrate the refractometer the first time and remember to get it up the correct water temp of your tank you will be fine. Always make sure you checks it's calibration every few months. The swing arm ones are not reliable.
     
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  13. reef addict

    reef addict

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    thanks i must actually check its calibration.
     
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