Refractometer - what am I doing wrong?

[WhiteRaven]

I have a refractometer from brs with calibration fluid. I have to calibrate before every use as it usually needs it. Even from one day to the next. I've gotten to the point of double checking calibration afterwards too to be sure it didn't adjust on me again which it has a couple of times without any bumping.

I try to be careful not to bump it in any way or tip it.

Is this normal? Am I doing something wrong?

 

[Crabs McJones]

How long after putting the solution on the refractometer are you waiting to check your reading? If it's the ATC (temp compensating) It's best to wait for 45 seconds to a minute before checking the results to give the refractometer time to adjust.

 

[PDR]

That doesn't sound right to me. I check mine every couple of months and rarely does it need recalibration.

 

[jgvergo]

One common mistake is if you have air bubbles in between the glass and the plastic plate. Make sure that you lower the plate carefully to ensure no bubbles. Also, clean the refractometer with RO water and a clean microfiber cloth (BRS supplies one with their device). It's very sensitive to dirt and other impurities like dried salt.

 

[redfishbluefish]

I only have one thing to say:

Lubricate Your Refractometer

 

[Crabs McJones]

I only have one thing to say:

Lubricate Your Refractometer

Shame on me, I didn't even think of that

 

[Timfish1]

One common mistake is if you have air bubbles in between the glass and the plastic plate. Make sure that you lower the plate carefully to ensure no bubbles. Also, clean the refractometer with RO water and a clean microfiber cloth (BRS supplies one with their device). It's very sensitive to dirt and other impurities like dried salt.

+1 Just wiping a refractometer off can leave a film of salt behind that can really throw off a reading.

 

[WhiteRaven]

How long after putting the solution on the refractometer are you waiting to check your reading? If it's the ATC (temp compensating) It's best to wait for 45 seconds to a minute before checking the results to give the refractometer time to adjust.

Wow. Temp matters? I thought that was only for hydrometers. Does it apart matter if my calibration fluid is a different temp than the water I'm testing?

I have the ATC one. Not sure if it is temp correcting but I'll least the minute to see.

 

[Crabs McJones]

Wow. Temp matters? I thought that was only for hydrometers. Does it apart matter if my calibration fluid is a different temp than the water I'm testing?

I have the ATC one. Not sure if it is temp correcting but I'll least the minute to see.

Yes, at different temperatures you will get different readings. So if you have the ATC one, it compensates for the temperature difference, but you need to give it 45 seconds to a minute to adjust.
From an article from Randy Holmes-Farley

Temperature and Refractive Index: ATC

It turns out that refractive index is highly dependent on temperature. When using a refractometer that does not account for this effect, temperature changes can be a large source of errors. Most liquid materials expand slightly when heated and shrink when cooled. For a given material, light can pass through it more easily when it is expanded, so the index of refraction falls when materials are warmed. However, the magnitude of this effect is different for every material, and refractometers must somehow take this into account.

Handheld refractometers account for temperature by employing a bimetal strip inside them. This bimetal strip expands and contracts as the temperature changes. The bimetal strip is attached to the optics inside the refractometer, moving them slightly as the temperature changes. This movement is designed to exactly cancel temperature’s effects on refractive index, and generally does a very good job IF the refractometer is designed to cancel out the temperature effects of the specific material being analyzed.

Because many refractometers are designed to use aqueous (water) solutions, the bimetal strip can be designed to account for the change in refractive index of aqueous solutions with temperature, although it may not be perfect in some situations because salts and other materials in the water can change temperature’s effects on refractive index by a small extent (or possibly to a large extent for very concentrated solutions, such as 750% sugar in water, but seawater is not in that category). Other details of this compensation may cause it to be imperfect (for example, the bimetallic strip provides a linear correction while the true temperature effect may be nonlinear), but those issues are beyond the scope of this article, and in general automatic temperature compensation (ATC) is a very useful attribute for aquarists using refractometers.

 

[WhiteRaven]

So I'll start cleaning with rodi water, make sure all the bubbles are out, wait a minute before checking the reading so that temp can adjust and use the same light.

I was using the provided cloth and wiping it dry. I was calibrating by my mixing station then checking by DT and finally checking QT's all in different rooms so different lights. Maybe I'll use my phone light every time since I'll always have it with me in each room. I'm curious curious now to put calibration solution in it and view it in each room light source, keeping same calibration solution in, to see if it changes.

The hinge lubrication is a good call out. Mine is still pretty new and moves very easily and passed the tests in the post you linked. So I don't think it is that issue in my case.

 

[WhiteRaven]

Yes, at different temperatures you will get different readings. So if you have the ATC one, it compensates for the temperature difference, but you need to give it 45 seconds to a minute to adjust.
From an article from Randy Holmes-Farley

Temperature and Refractive Index: ATC

It turns out that refractive index is highly dependent on temperature. When using a refractometer that does not account for this effect, temperature changes can be a large source of errors. Most liquid materials expand slightly when heated and shrink when cooled. For a given material, light can pass through it more easily when it is expanded, so the index of refraction falls when materials are warmed. However, the magnitude of this effect is different for every material, and refractometers must somehow take this into account.

Handheld refractometers account for temperature by employing a bimetal strip inside them. This bimetal strip expands and contracts as the temperature changes. The bimetal strip is attached to the optics inside the refractometer, moving them slightly as the temperature changes. This movement is designed to exactly cancel temperature’s effects on refractive index, and generally does a very good job IF the refractometer is designed to cancel out the temperature effects of the specific material being analyzed.

Because many refractometers are designed to use aqueous (water) solutions, the bimetal strip can be designed to account for the change in refractive index of aqueous solutions with temperature, although it may not be perfect in some situations because salts and other materials in the water can change temperature’s effects on refractive index by a small extent (or possibly to a large extent for very concentrated solutions, such as 750% sugar in water, but seawater is not in that category). Other details of this compensation may cause it to be imperfect (for example, the bimetallic strip provides a linear correction while the true temperature effect may be nonlinear), but those issues are beyond the scope of this article, and in general automatic temperature compensation (ATC) is a very useful attribute for aquarists using refractometers.

Very interesting. Thanks!

I like to mix the water to have on hand for emergencies. But wait to heat it until before water change to save electricity. Is there a range where the water temp is too extreme to be adjusted by the wire accurately? My house is 73. The water is in a brute can in the basement so say 68 degrees. Is that too cold for the temp correcting refractometer to handle? I run my display tank at 78.

 

[HolisticBear]

I have a refractometer from brs with calibration fluid. I have to calibrate before every use as it usually needs it. Even from one day to the next. I've gotten to the point of double checking calibration afterwards too to be sure it didn't adjust on me again which it has a couple of times without any bumping.

I try to be careful not to bump it in any way or tip it.

Is this normal? Am I doing something wrong?

Which refractometer? The BRS brand or the Red Sea? The Red Sea one is infamous for losing calibration within minutes and many reefers across the planet have thrown it in the garbage after much frustration.

The BRS brand has a good reputation. BRS also put out a bad lot of calibration solution awhile back, but promptly pulled it from the shelves, on the off chance you're comparing two different bottles of calibration solution.

 

[Crabs McJones]

Very interesting. Thanks!

I like to mix the water to have on hand for emergencies. But wait to heat it until before water change to save electricity. Is there a range where the water temp is too extreme to be adjusted by the wire accurately? My house is 73. The water is in a brute can in the basement so say 68 degrees. Is that too cold for the temp correcting refractometer to handle? I run my display tank at 78.

It should be able to compensate from 10 to 30 degrees centigrade or 52 to 86 farenheit

 

[Dr. Reef Verified Sponsor]

Almost all products/standards say to keep solution at 76-78F to calibrate. Also all saltmix recommend the same temp for mixing.
I would bring the refractometer and standard solution at room temp before calibrating. Also rinse the prism on the refrac with running rodi water.
Let solution sit for 1 min before adjusting.

I use 2 little fishes standard. my refrac was calibrated probably 2 years ago and it hardly ever drifts.

 

[WhiteRaven]

The temp seemed to be the main issue. Waiting 1 minute for the refractometer has worked well. Everything stays right on.

I used my phone light each time and secondarily tried with different room lights. I didn't notice any difference other than some lights make the line easier to see.

I had generally tried to keep air bubble minimal before but have been more picky about it now too.

Thanks again everyone. My fish and Coral thank you too that they will have less stress.