DIY 35ppt refractometer calibration fluid with normal salt water?

Michel

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Because i'm always afraid of the calibration fluid getting inaccurate after a few calibrations caused by evaporation in such a small bottle, I always buy a new bottle when I used it about half way. (I have lost some fish and corals a few years ago caused by my 35ppt callibration flued being way off).

So can't I just fill a 1 liter bottle with RODI water and add salt to make it exact 35ppt? (testing it with a new bought callibration fluid).

I think this solution will be way more stable holding 35ppt in the long term than those small bottles that you buy.

I would like to hear if this is a good idea or not.
 
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Randy Holmes-Farley

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Michel

Michel

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What salt would you add? Cannot be salt mix because it holds a lot of water when "dry", and cannot be NaCl because that doesn't match seawater 35 ppt properties.

What you can do is use specific concentrations of NaCl for specific device calibrations:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
Thank you for the fast reply!

I have read somewhere before that you can't use mix salt for this but why can't you use NaCl?
Could you please explain me what u mean with NaCl not matching seawater 35ppt properties?

For the refractometer only salinity matters right? or am I wrong?

I was thinking really simple:

1. Callibrate refractometer with normal 35ppt reaction fluid.
2. Add 1L RODI water in bottle.
3. Add NaCl till my refractometer reads 35ppt.
4. Use this bottle for callibrate my refractormeter back to 35ppt.
 
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Randy Holmes-Farley

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Thank you for the fast reply!

I have read somewhere before that you can't use mix salt for this but why can't you use NaCl?
Could you please explain me what u mean with NaCl not matching seawater 35ppt properties?

For the refractometer only salinity matters right? or am I wrong?

I was thinking really simple:

1. Callibrate refractometer with normal 35ppt reaction fluid.
2. Add 1L RODI water in bottle.
3. Add NaCl till my refractometer reads 35ppt.
4. Use this bottle for callibrate my refractormeter back to 35ppt.

You can do that (but you do not end up making 35 ppt NaCl), which is exactly what my recipe does in the article.

I suggest reading it before asking more questions along these lines.

in short, , you measure the salt weight or volume yourself. You need not have an existing standard, and if you do, you need not assume that it is actually accurate.
 

Randy Holmes-Farley

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I have a refractometer from Aqua Medic with the led on top.
May I ask why you ask this question? aren't all refractometers sort of the same?

No, they are not.

A few are true seawater refractometers, and many are brine (NaCl) refractometers.

They can still both be properly calibrated using an accurate 35 ppt standard, but the brine refractometers cannot be calibrated properly for 35 ppt seawater using pure fresh water, despite directions to do so.

This has more:

 
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Michel

Michel

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No, they are not.

A few are true seawater refractometers, and many are brine (NaCl) refractometers.

They can still both be properly calibrated using an accurate 35 ppt standard, but the brine refractometers cannot be calibrated properly for 35 ppt seawater using pure fresh water, despite directions to do so.

This has more:

Thank you for clarification, now I understand the question.

You can do that (but you do not end up making 35 ppt NaCl), which is exactly what my recipe does in the article.

I suggest reading it before asking more questions along these lines.

in short, , you measure the salt weight or volume yourself. You need not have an existing standard, and if you do, you need not assume that it is actually accurate.
Thanks again and I will read and try that method.
 

piranhaman00

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I have a refractometer from Aqua Medic with the led on top.
May I ask why you ask this question? aren't all refractometers sort of the same?

No, the cheap ones need to be calibrated with 35ppt solutions.

VeeGee can and should be calibrated with DI water at 00ppt and are accurate through the whole range.
 
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Michel

Michel

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No, the cheap ones need to be calibrated with 35ppt solutions.

VeeGee can and should be calibrated with DI water at 00ppt and are accurate through the whole range.
The instructions that came with my refractormeter tells me to callibrate it with RODI water.
But when I callibrate it with 35ppt callibration fluid I read -3ppt on RODI.
So I just stick with 35ppt callibration fluid to be sure.
 
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piranhaman00

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The instructions that came with my refractormeter tells me to callibrate it with RODI water.
But when I callibrate it with 35ppt callibration fluid I read -3ppt on RODI.
So I just stick with 35ppt callibration fluid to be sure.

Yes because it is cheap and not accurate, you have to calibrate with 35ppt on those to get as close as possible.
 

Randy Holmes-Farley

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The instructions that came with my refractormeter tells me to callibrate it with RODI water.
But when I callibrate it with 35ppt callibration fluid I read -3ppt on RODI.
So I just stick with 35ppt callibration fluid to be sure.

A brine refractometer (most in the hobby) that is perfectly made and perfectly calibrated with RO/DI will necessarily read 35 ppt seawater as 36.7 ppt.

Turned around, if you perfectly calibrate a perfectly made brine refractometer with a perfect 35 ppt seawater solution to read 35 ppt on the refractometer, then when checking ro/di, it will read -1.7 ppt.

Regardless of whether a device is perfectly made or not, if you calibrate ANY refractometer with 35 ppt seawater, then it will be accurate for measuring 35 ppt seawater, and it is never wrong to do so, no matter what it reads in RO/DI.
 

gone_phishin

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so what calibration fluid are people using with the VeeGee refractometer?

i am tired of my cheap refractometer being off. i calibrate it every time i use it, and even minutes apart after calibration, i’ll get different results. i am about to buy the VeeGee, but i have now read that calibration fluids can be off too!

i need accuracy!
 

piranhaman00

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so what calibration fluid are people using with the VeeGee refractometer?

i am tired of my cheap refractometer being off. i calibrate it every time i use it, and even minutes apart after calibration, i’ll get different results. i am about to buy the VeeGee, but i have now read that calibration fluids can be off too!

i need accuracy!

Use RODI and calibrate to 0ppt :) works perfectly and stays calibrated for long periods of time, I check sometimes but it’s always on!
 

homer1475

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A brine refractometer (most in the hobby) that is perfectly made and perfectly calibrated with RO/DI will necessarily read 35 ppt seawater as 36.7 ppt.

Turned around, if you perfectly calibrate a perfectly made brine refractometer with a perfect 35 ppt seawater solution to read 35 ppt on the refractometer, then when checking ro/di, it will read -1.7 ppt.

Regardless of whether a device is perfectly made or not, if you calibrate ANY refractometer with 35 ppt seawater, then it will be accurate for measuring 35 ppt seawater, and it is never wrong to do so, no matter what it reads in RO/DI.

Use RODI and calibrate to 0ppt :) works perfectly and stays calibrated for long periods of time, I check sometimes but it’s always on!
You should never calibrate to 0 with RO/DI as Randy stated above why.

There is a nice article written by Randy (I believe?) that explains why a single point of calibration is used, and why it needs to be close to what your measuring.


Every refractometer I've ever used said to calibrate with RO/DI, but that is just plain wrong for our application.
 
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