ATC Refractometer needs constant recalibration

[Jcon82]

Hi All,

I'm fining my ATC refractometer is out of calibration every time I use it. I check with Brightwell 35ppt solution and it is typically 3-5ppt off.
Is this normal for refractometers or should I look into getting a better tool?

 

[Garf]

Hi All,

I'm fining my ATC refractometer is out of calibration every time I use it. I check with Brightwell 35ppt solution and it is typically 3-5ppt off.
Is this normal for refractometers or should I look into getting a better tool?

You sure it’s the refractometer and not the calibration solution?

 

[CWalters]

Hi All,

I'm fining my ATC refractometer is out of calibration every time I use it. I check with Brightwell 35ppt solution and it is typically 3-5ppt off.
Is this normal for refractometers or should I look into getting a better tool?

I've had to recalibrate mine twice. I usually try to do it every few weeks to make sure it is good still.

Agreed with Garf, do you shake up your calibration solution before adding it on?

 

[Wiskey]

I bought a calibration solution that said to burn off the first 5 drops because the fluid stays in the tip and drys making the first couple drops incorrect. I started doing this and was shocked!!!! I'd had my refractometer off all this time, and inconstantly off too.

Now I do the regular calibration and then check with RODI to make sure it's very close to 0, if it's not I redo the calibration.

Whiskey

 

[Roli's Reef Ranch]

I used to use that exact refractometer and had the same issues, I have the RedSea one and it had the same issue, especially if you're using it "cold." Now I use a Tropic Marin hydrometer (the only thing I really trust) and a Hanna salinity checker for convenience on multiple systems. I find it needs far less calibration.

 

[Borat]

I used to use that exact refractometer and had the same issues, I have the RedSea one and it had the same issue, especially if you're using it "cold." Now I use a Tropic Marin hydrometer (the only thing I really trust) and a Hanna salinity checker for convenience on multiple systems. I find it needs far less calibration.

You need the temperature of refractometer and solution to be near the same consistent value (e.g. 22 degrees celsius)... Variation in temperature will lead to variation in readings.

I store my refractometer outside - and I have to wait for a couple of hours for it to get to room temperature..

 

[Garf]

You need the temperature of refractometer and solution to be near the same consistent value (e.g. 22 degrees celsius)... Variation in temperature will lead to variation in readings.

I store my refractometer outside - and I have to wait for a couple of hours for it to get to room temperature..

Ok, obvious question coming up.
Why do you keep your refractometer outside? Lol

 

[Randy Holmes-Farley Verified Community Expert]

I've had to recalibrate mine twice. I usually try to do it every few weeks to make sure it is good still.

Agreed with Garf, do you shake up your calibration solution before adding it on?

Are you suggesting he should or should not shake it? Shaking a salinity calibration solution should not be needed nor desirable, since both air bubbles and floating solids may mess it up, and salinity calibration solutions will not separate into different liquid layers on sitting.

 

[Jcon82]

You need the temperature of refractometer and solution to be near the same consistent value (e.g. 22 degrees celsius)... Variation in temperature will lead to variation in readings.

I store my refractometer outside - and I have to wait for a couple of hours for it to get to room temperature..

I keep it my office and do all testing there rather than the fish room that is slightly cooler. I also let the calibration fluid and samples sit on the tool for several minutes to equalize temps.

 

[Jcon82]

I bought a calibration solution that said to burn off the first 5 drops because the fluid stays in the tip and drys making the first couple drops incorrect. I started doing this and was shocked!!!! I'd had my refractometer off all this time, and inconstantly off too.

Now I do the regular calibration and then check with RODI to make sure it's very close to 0, if it's not I redo the calibration.

Whiskey

I'll try burning off a few drops going forward.

 

[Randy Holmes-Farley Verified Community Expert]

To be honest, I don't see a good explanation of how either evaporation during testing or temperature issues can make it be off every time. It may be the screw is loose and it moves the calibration between uses.

Is it always off in the same direction, and does it read high or low?

 

[Jcon82]

To be honest, I don't see a good explanation of how either evaporation during testing or temperature issues can make it be off every time. It may be the screw is loose and it moves the calibration between uses.

Is it always off in the same direction, and does it read high or low?

I should document the calibration issue but if I recall it tends to read low.

 

[Randy Holmes-Farley Verified Community Expert]

I should document the calibration issue but if I recall it tends to read low.

Knowing if it is always in the same direction would help. I think a loose calibration screw is most likely if it varies up and down. Not many other explanations can explain that sort of variability.

An ATC refractometer should account for temp issues even during calibration, if it is within its calibration range, but it may not work perfectly. Getting the tank water, calibration fluid, and the refractometer all at about the same temp (let them sit in the same room for an hour or more) should eliminate temp as a factor, even if the ATC feature is poorly functioning.

 

[Garf]

I should document the calibration issue but if I recall it tends to read low.

Are you tweaking the screw to get the RODI to read zero, after you’ve tweaked it to get the 35ppt using the solution?

 

[Jcon82]

Are you tweaking the screw to get the RODI to read zero, after you’ve tweaked it to get the 35ppt using the solution?

I have not done that.

 

[CWalters]

Are you suggesting he should or should not shake it? Shaking a salinity calibration solution should not be needed nor desirable, since both air bubbles and floating solids may mess it up, and salinity calibration solutions will not separate into different liquid layers on sitting.

Good to know if that's the case.. I use the BRS Refracto Juice and that's the first thing it recommends

 

[Randy Holmes-Farley Verified Community Expert]

Good to know if that's the case.. I use the BRS Refracto Juice and that's the first thing it recommends

#1 just goes to show that folks should not go to BRS for chemistry-related advice. It makes no positive sense, and I can even see it causing issues.

 

[Borat]

Ok, obvious question coming up.
Why do you keep your refractometer outside? Lol

wife does not like all kinds of useless things to be indoor..

 

[Borat]

wife does not like all kinds of useless things to be indoor..

..and unless you are Chuck Norris - you never argue with your Kazakistan wife!

 

[Miami Reef]

#1 just goes to show that folks should not go to BRS for chemistry-related advice. It makes no positive sense, and I can even see it causing issues.

So I shouldn’t shake the DIY NaCl 35ppt that I made with your recipe either?

I always thought that water would condense on the lid, leaving saltier water in the solution. My common sense always told me to shake it prior.