Setting your Refractometer

Discussion in 'Test Kits, Controllers, Reactors and Dosers' started by mytank, 28 Oct 2011.

  1. mytank

    mytank

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    So I have a profilux but it's sitting in my study for now...

    What I do have as well is a Refractometer, but I can't seem to get the dam thing set properly.

    If I use some RO water and test it then it reads "0" which is right. However the other day when I was at Idol I ***THINK*** it was Rob that told me not to use RO water but to use proper salt water at 1025 and set it that way. He gave me a sample a while ago of perfect 1025 water and I set the Refractometer to that.

    When I test my water at Temp 25.5 I get 1023 / 1022. I use Rob's sample that he gave me (I stored it at room temp sample is about a two months old, kept in a cool dark place in a plastic bottle) - I get 1023 on his sample (which is suppose to be 1025).

    So I take my Refractometer and again test RO water and get a reading of 0.

    How do you guys set your Refractometers ? I would like to know so I an get this once and for all set. The make of the Refractometer is a Reef Octopus.

    Thank you
     
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  3. Tony

    Tony

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    Does your meter have ATC (automatic temperature compensation)?
     
  4. gavster

    gavster

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    Tagging
     
  5. Michael B

    Michael B

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    Also tagging on this one
     
  6. seank

    seank

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    Me three. Bought a refracto not too long ago, and still have not used it, as I do not know what to set it to, or rather what to compare it too
     
  7. mytank

    mytank Thread Starter

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    I have no idea what it has all I know is I got it from marco aka The waterboy. Its a reef octopus how would I find out?

    Sent from my SGH-i917 Microsoft Windows Phone 7 (Mango) using Board Express
     
  8. Tony

    Tony

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    OK, if its a reef octopus then it doesnt have ATC. Get your RO unit running for about 2 minutes to flush it till you have a 0 TDS reading. Now add the water to a clean, sealable vial and fill it with RO water. Place the vial in your sump in the water, in a low flow area for about ten minutes to warm up. The tube needs to be well sealed so it doesnt take on salt water. After ten minutes Take some of the water which has warmed up to your tanks temp and place it on the refractometer and with the small screwdriver turn the screw on top of the meter till it rests on zero. Your meter is now calibrated.

    Another alternative is to buy a bottle of distilled water and rest it standing up in your sump, but not so that it's completely submerged. You will have to leave it for about 20 minutes as they are usually 750ml bottles and it needs time to warm up
     
  9. Tony

    Tony

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    Looking through the meter there is a blue and clear markings indicating the reading. The line where the blue and clear meet must rest on zero
     
  10. Nemos Janitor

    Nemos Janitor

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    More important than the water sample temperature is the temperature of the refractometer.

    The small amount of water (1 or 2 drops) when placed on the refractometer will very quickly become the same temperature as the refractometer. It is also important to only hold the refractometer on the rubber grip. This grip insulates the instrument from ones body heat and stops the temp of the instrument rising.

    Most refractometers are calibrated at a temp of 20 deg C which is normal room temperature.

    So when a SG reading of 1,0266 is tested at a temp of 20C the actual SG at a temp of 25C is 1,0252. These figures relate to a salinity of 35.5 ppt. We should always try and talk in terms of salinity, rather than SG because Salinity is not temperature dependant and SG is.

    The errors @mytank is experiencing when calibrating with the 1 .025 reference fluid is because the refractometer needs to be at 20C. If he calibrates the refractometer at a temp of 25C then the SG will show lower by about .0014
     
    Last edited by a moderator: 26 Nov 2015
  11. mytank

    mytank Thread Starter

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    Looks like I am going to have to get my profilix up and running .....

    Sent from my SGH-i917 Microsoft Windows Phone 7 (Mango) using Board Express
     
  12. Nemos Janitor

    Nemos Janitor

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    Let me explain the difference between a normal refractometer and a ATC one. But first we need to understand that a refractometer measures refractive indexes of light and not the amount of salinity or the specific gravity (SG). So their are other influences that could affect the readings like water clarity, amount of iron's etc. We must also understand that RO water ( or pure water) has a SG of varying values according to the temperature and altitude. Mass, Weight, Density or Specific Gravity of Water at Various Temperatures. The same will apply for other reference solutions. You will notice on all calibration solutions, be they pH, redox, SG, etc that there is a reference temperature that the solution is correct at. This is important in the calibration accuracy.

    Now that we understand that temperature plays a big part in SG what part does it play in salinity? Temperature does not affect salinity because salinity is measured in PPT. That means that the amount of salts in the solution are measured in parts per thousand. In the case of our aquariums, and the average global reef salinity, at an average of 35.5 ppt. This relates to a weight ( not 100% accurate but very close) of 35.5kg salt to 964.5kg RO water per 1000 litres of seawater.

    How does a ATC refractometer work?
    An ATC refractometer has a small bi-metal strip inside that moves the reading scale as the temperature changes. A normal refractometer does not have this bi-metal strip to move the scale after calibration.

    On the reading scale there is normally an indication of the calibration temperature. In most cases the calibration temperature is 20C and the scale would be marked 20C or 20/20. It is important to calibrate the refractometer when the temperature of the instrument is at 20C. This applies whether you are using RO water or a reference solution as well as whether it is a ATC refractometer or not.

    When using a refractometer that does not have ATC the instrument must be at the calibration temperature indicated on the scale. This is for the calibration and sample reading.

    When using a ATC refractometer the instrument must be calibrated at 20C ( or the indicated temp). The ATC will now compensate for temperature changes in the instrument. This means that instrument will read correctly at temperatures between 10 and 30C. Let me clarify that better. The instrument must be calibrated at the "instruments" calibration temperature. Not the water to be tested temperature as the small amount of water will soon come into equilibrium with the instrument temperature. Once calibrated the ATC will compensate for temperature changes of the instrument. This is useful for measuring samples in environments outside of the 20C

    Hope this explains some of the misunderstandings around refractometer calibration and ATC.

    We can go much deeper into science but for most part it is the consistency of the tests that are important to the aquariust and not so much the exact SG or PPT. Where issues arise is if the calibration and sample readings are varied and corrective action is taken on readings based on inconsistencies in testing and temperature.
     
    Last edited: 29 Oct 2011
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  13. Nemos Janitor

    Nemos Janitor

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    On a related topic is the water parameters of other key elements. We see aquarists state numbers of test parameters. All are quite honestly meaningless with out a reference temp of 20C and a salinity outside 35.5 PPT. We need to set a standard that all understands and quote parameters at the normal room temperature of 20C and salinity of 35.5 PPT.
     
  14. mytank

    mytank Thread Starter

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    Thank you Keith I am trying to understand something are you saying I should first get the water temp down to 20 and then do all the tests like the salinity and water parameters tests?

    Sent from my SGH-i917 Microsoft Windows Phone 7 (Mango) using Board Express
     
  15. Nemos Janitor

    Nemos Janitor

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    No. You need to calibrate your refractometer/instrument when the instrument is at 20C. The water temperature is irrelevant.

    If the refractometer is then an ATC refractometer the changing temperature of the instrument and testing solution is the irrelevant as the ATC will do the compensation. But remember that the reading is related at 20C.

    If the refractometer is not an ATC then the calibration temperature of the instrument needs to be the same for the calibration and testing solution. Remember that the 1.025 reference solution you got from @Bob the (reef)builder is a solution at 20C and for correct calibration needs to be calibrated on an instrument at 20C

    With RO water you can calibrate a non ATS instrument as @Tony suggested. But the instrument needs to be at the same temp for both tests and the SG needs to be stated to the testing instruments temperature. So you will need to use a table to revert the actual SG back to the 20C reference. Or obtain the actual salinity in PPT terms.
     
    Last edited by a moderator: 26 Nov 2015
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  16. wouterloosman

    wouterloosman

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    Measuring salt levels in a marine aquarium

    Also don't forget that your profilux is measuring Density and a Refractometer is measuring Specific Gratify.

    I also was really confused by that a while ago, till I found the following document:
    Measuring salt levels in a marine aquarium

    At the end of the document is a nice conversion table.

    Wouter
     
  17. Nemos Janitor

    Nemos Janitor

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    Yes that artical sums up most of what I say except that it is assumed that the tests and refrences are done at one atmospher. (sea level)

    Conductivity will also vary at different depths, temperatures and altitudes and substances in the water. DO also plays a role in conductivity. Think in terms of REDOX. So perhaps conductivity is not the bees knees.

    It all boils down to understanding what you are measuring. Be it SG, salinity, conductivity or density. But above all, understanding what the testing instrument is telling you and relating that to your goal results keeping in mind the relationship and influences of other parameters and not confusing them with " target parameters" that are stated in a compleatly different context.

    As room temperature is about 20C it makes sense to calibrate all equipment at that temperature and refer to readings at that temperature.

    If the calibration reference solutions are specific at 25C, and the Aquatronica and profilux are, then the probe/ instrument also needs to be at 25C. A typical pH reference can alter from 7.01 at 20C to 6.89 at 30C

    As one of the largest users of Aquatronica in the world a few years ago, I have had a few debates over the accuracy of the Aquatronica density probes. @LikesFish might like to confirm and comment on this discussion. Yes we have done this many times over the years. @Reef Maniac may also recall.

    Density probes fall out of calibration very quickly and are influenced by other electrical currents in the tank. These currents come from pumps, T5 ballasts etc. IMO these probes should be only used as a guide line and not a reference to adjust salinity or other parameters. Something like one uses a petrol indicator in a car. It tells you the tank is half full but not the exact no of litres in the tank.
     
    Last edited by a moderator: 26 Nov 2015
  18. Jeann1

    Jeann1

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    Nice Article.. Great Read..

    I also had the normal type refractometers, until i realized there was a fault with my unit.

    Went out and did some recearch and decided on going with the new D-D Refractometer..

    In the brochure, it explains that normal refractometers are calibrated on a "salty solution" not to say that it is not salt water.. solution might have the same spesific gravity, but still not salt water.

    So the new range of D-D refractometers, are salt water (sea water) calibrated. The viewing glass is also different, it has SG on the one side and ppt on the other. Completely different than normal refractometers...
     
  19. Donovan

    Donovan

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    i used distilled water
     
  20. Bob the (reef)builder

    Bob the (reef)builder

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    Absolutely, the water changes to the temp of the instrument almost instantaniously.

    Take your refractometer out of a 45degree bakkie or a 10 degree garage in mid winter, and see how wild your readings can be.;)
     
  21. Suhayl

    Suhayl

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    Jean I dont know how other refratrometers look but my Erma (made in Japan) has Sg on left and Ppt on the right side. I paid R235 on my last visit to India. I still prefer my Sera hydrometer which gives accurate readings.
     
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