Use calibration fluid they said!

[lost66]

What is "Randy's formula"?

 

[Randy Holmes-Farley]

What is "Randy's formula"?

http://reefkeeping.com/issues/2004-06/rhf/index.htm

 

[Justdrew]

Take your time doing the calibration. Let the probe sit in the fluid for 10 minutes and calibrate 7.0 then do the 10.0 the same way. Repeat the same process about 5 times. Also check the temp of the fluid and adjust the calibration as per the chart on the back of the package.

Be wary of taking so long to calibrate. The 7.0 packet is not an issue, but the 10.0 packet will drop in pH as it is exposed to CO2 in the air.

 

[capted]

Be wary of taking so long to calibrate. The 7.0 packet is not an issue, but the 10.0 packet will drop in pH as it is exposed to CO2 in the air.

Good point. I have timed it for about 45 minutes total to calibrate. Opened 2 new packets of 7.0 and 10.0 and the meter was still calibrated perfectly. My own little controlled experiment. Ha. Not sure about any longer in time though. Maybe next time I will see how long it takes for the 10.0 to start dropping. Anybody try to test that theory?

 

[lost66]

http://reefkeeping.com/issues/2004-06/rhf/index.htm

Thanks!

 

[Hellic]

http://reefkeeping.com/issues/2004-06/rhf/index.htm

Hey Randy I just wanted to clarify. I read the article and noted that the refractometer standard is 3.64 per 96.35ml of fresh water (rodi? Tap?) But since my refractometer measures in specific gravity rather than ppt, should i use the specific gravity standard instead for hydrometers? Or should I still use the refractometer standard and calibrate it to 1.0264. Thanks for the clarification.

 

[Randy Holmes-Farley]

Hey Randy I just wanted to clarify. I read the article and noted that the refractometer standard is 3.64 per 96.35ml of fresh water (rodi? Tap?) But since my refractometer measures in specific gravity rather than ppt, should i use the specific gravity standard instead for hydrometers? Or should I still use the refractometer standard and calibrate it to 1.0264. Thanks for the clarification.

No, use the refractometer standard using RO/DI, and preferably weighing the salt. Set the refractometer to sg = 1.0264, or as close as you can get to that.

" 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water. "

FWIW, the different standards relate to the device used (and how they determine salinity), not the units they report for 35 ppt seawater (sg = 1.0264, conductivity = 53 mS/cm)..

 

[Hellic]

No, use the refractometer standard using RO/DI, and preferably weighing the salt. Set the refractometer to sg = 1.0264, or as close as you can get to that.

" 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water. "

FWIW, the different standards relate to the device used (and how they determine salinity), not the units they report for 35 ppt seawater (sg = 1.0264, conductivity = 53 mS/cm)..

Yeah thats where I was getting a little confused. Thank you for the clarification!

 

[Gtinnel]

I’ve been using Randy’s recipe for a while now and it has always worked perfectly.

One thing I always do is make an amount 10 or more times the recipe just so small measuring errors aren’t as important. It makes a lot of fluid but it still costs essentially nothing to make.

 

[TastesLikeChicken]

Anyone have experience with BRS calibration fluid?

 

[Tobin VP]

RO/DI is inaccurate for many refractometers. it is not a guess. If they are correctly made, they must be inaccurate when calibrated with RO/DI.

@Randy Holmes-Farley: Just spent the last week plus with back and forth emails with Red Sea. They indicated that their refractometer is designed to calibrate with RODI water. I'm going through a complete testing process now to get to the bottom of this further. More to come in another post.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley: Just spent the last week plus with back and forth emails with Red Sea. They indicated that their refractometer is designed to calibrate with RODI water. I'm going through a complete testing process now to get to the bottom of this further. More to come in another post.

They do claim it is a true seawater refractometer, and as such, it can be calibrated with RO/DI, assuming it is perfectly made and calibrated.

it can also be calibrated with a 35 ppt standard, like my DIY, which allows one to confirm 35 ppt, even if the refractometer is not perfectly made.

Seawater Refractometer - Red Sea Salinity test for marine aquariums

Red Sea’s Seawater Refractometer offers exceptional accuracy, for measuring the absolute salinity of seawater Specifically designed for saltwater aquariums

www.redseafish.com

High-Accuracy Seawater Refractometer

Most refractometers used within the aquarium hobby are not specifically designed for reef aquariums and use an algorithm for the measurement of brine (NaCl – rather than seawater) and at a temperature of 15oC/59 0F rather than 25oC/77 0F. Thus, a measurement deviation of up to 1.5ppt is possible, which can have a significant adverse effect on coral growth and coloration.

 

[Big Smelly fish]

I been using two old Milwaukee refractor for the past 20 or almost 20 years. The instructions says use distilled water to calibrate. I use to water and hardly ever need to adjust and they are both point on with each other. I have never used calibration fluid.

 

[Tobin VP]

They do claim it is a true seawater refractometer, and as such, it can be calibrated with RO/DI, assuming it is perfectly made and calibrated.

Yes I definitely agree ... "if perfectly made" ... from a design perspective ... but what about manufacturing variations?

Clearly if it is a brine refractometer you have no hope of calibrating at 0 ppt (RODI) and then extrapolating out to typical measurements as the slope of the calibration would be in sufficient enough errors. I have also assumed (maybe wrongly) that due to manufacturing tolerances that the slope could still be affected ... so always best to calibrate near your target at 35 ppt no matter what.

It must then be true that as long as the refractometer is a seawater refractometer that these manufacturing variations typically do not lead to significant variations in the slope of the calibration and therefore seawater refractometers typically could be calibrated with RODI?

 

[Randy Holmes-Farley]

I been using two old Milwaukee refractor for the past 20 or almost 20 years. The instructions says use distilled water to calibrate. I use to water and hardly ever need to adjust and they are both point on with each other. I have never used calibration fluid.

You just have to be careful when believing those claims. In this case, the Milwaukee is a true seawater refractometer, and so it can properly be done either way, but brine refractometers make the same claim and yet fail the test in actual seawater.

i personally would recommend checking the Milwaukee at least once in a seawater standard since otherwise you have no idea if it was made correctly or not.

 

[Randy Holmes-Farley]

Yes I definitely agree ... "if perfectly made" ... from a design perspective ... but what about manufacturing variations?

Clearly if it is a brine refractometer you have no hope of calibrating at 0 ppt (RODI) and then extrapolating out to typical measurements as the slope of the calibration would be in sufficient enough errors. I have also assumed (maybe wrongly) that due to manufacturing tolerances that the slope could still be affected ... so always best to calibrate near your target at 35 ppt no matter what.

It must then be true that as long as the refractometer is a seawater refractometer that these manufacturing variations typically do not lead to significant variations in the slope of the calibration and therefore seawater refractometers typically could be calibrated with RODI?

Yes, I include manufacturing variances in the "made properly" description, and it is never wrong to calibrate, or at least check, a refractometer intended for 35 seawater with a good 35 ppt standard.

I've not seen anyone check a lot of any brand of refractometer for random differences, but the relative high uncertainty the manufacturers claim (a whopping +/- 2 ppt for the Milwaukee, for example) may be large for that reason.

 

[ying yang]

Screenshot from article randy posted in post 32 above, red sea keep saying there's is designed for seawater and keep mentioning " sea water " and " nsw" so does this mean If test true natural sea water " nsw" at 25° then its fine to use, but what about testing "asw" which I use and alot of other reefers use artificial sea water " asw" so @Randy Holmes-Farley are they saying its only accurate to use " nsw" ,just curious is all on your thoughts

 

[PigDaddyF15E]

Jumping in here. I'm not a chemist...I think the issue is that it's so easy to introduce some type of error. Make your own is great...until you get the measurements wrong (I used Randy's Recipe with great success). Buy a premade? who knows if it's right. Convert from SG to PPT to Brix or whatever...make an error (temp correction? The fact it's not exactly "that easy")


Isn't one of the best ways to tell the gravity is to use something like this? Not that these aren't without error...but aren't they the most "scientific" of the lot?

once you correct for temp (I have a website bookmarked)....you know what the gravity is...then you calibrate your refractometer.

 

[Tobin VP]

Screenshot from article randy posted in post 32 above, red sea keep saying there's is designed for seawater and keep mentioning " sea water " and " nsw" so does this mean If test true natural sea water " nsw" at 25° then its fine to use, but what about testing "asw" which I use and alot of other reefers use artificial sea water " asw" so @Randy Holmes-Farley are they saying its only accurate to use " nsw" ,just curious is all on your thoughts

Bottom line is I think you are fine as long as your "asw" closely simulates seawater.

More discussion:

Its my understanding reading @Randy Holmes-Farley articles that small variations in ionic composition of seawater does not change refractive index (which is what we care about) in appreciable ways. There are possibly a couple of exceptions for very high or very low Mg content - but that would not be typical. See section "Refractive Index and Ion Imbalances in Seawater" at:

https://reefkeeping.com/issues/2006-12/rhf/index.php

Note: Randy has a DIY recipe of just using table salt to make a salinity standard solution to calibrate to:

https://reefkeeping.com/issues/2004-06/rhf/index.php

I point this out because it shows that you do not need the exact composition of ions ... but only the correct resulting refractive index. This is a great standard to calibrate or check with since it is easy to make at home with pure table salt. Randy figured out what concentration of NaCl results in a specific index that is tied to the target concentration in seawater that we would typically measure at or calibrate to, i.e. 35 ppt.

Also, Red Sea assumes "seawater use" when they design/build their device and this is why "sometimes" you can get away with calibrating to 0 ppt RODI only. Other refractometers designed for other uses such as brine can be made to work by calibrating near our operating condition (35 ppt seawater) or otherwise you will pick up significant errors. As Randy points out in his article, it is good practice in this case to calibrate to 0 ppt first then check that calibration at a standard such as 35 ppt. Once you do this then it is likely that calibrating to RODI only going forward for that device will continue to provide accuracy. If not then it shows a manufacturing variance and then you would need to account for that by calibrating to the 35 ppt. instead and not relying only on the RODI calibration. Randy goes through a discussion on offset and slope of the assumed linear calibration relationship. We have control over adjusting the offset but not slope of the linear relationship.

So you should be fine using the Red Sea Refractometer and calibrating to 0 ppt - assuming the "asw" is a salt mix that does a reasonable job simulating natural seawater. Maximum accuracy can be achieved with the additional check at a standard 35 ppt after calibrating at 0 ppt.

 

[ying yang]

Bottom line is I think you are fine as long as your "asw" closely simulates seawater.

More discussion:

Its my understanding reading @Randy Holmes-Farley articles that small variations in ionic composition of seawater does not change refractive index (which is what we care about) in appreciable ways. There are possibly a couple of exceptions for very high or very low Mg content - but that would not be typical. See section "Refractive Index and Ion Imbalances in Seawater" at:

https://reefkeeping.com/issues/2006-12/rhf/index.php

Note: Randy has a DIY recipe of just using table salt to make a salinity standard solution to calibrate to:

https://reefkeeping.com/issues/2004-06/rhf/index.php

I point this out because it shows that you do not need the exact composition of ions ... but only the correct resulting refractive index. This is a great standard to calibrate or check with since it is easy to make at home with pure table salt. Randy figured out what concentration of NaCl results in a specific index that is tied to the target concentration in seawater that we would typically measure at or calibrate to, i.e. 35 ppt.

Also, Red Sea assumes "seawater use" when they design/build their device and this is why "sometimes" you can get away with calibrating to 0 ppt RODI only. Other refractometers designed for other uses such as brine can be made to work by calibrating near our operating condition (35 ppt seawater) or otherwise you will pick up significant errors. As Randy points out in his article, it is good practice in this case to calibrate to 0 ppt first then check that calibration at a standard such as 35 ppt. Once you do this then it is likely that calibrating to RODI only going forward for that device will continue to provide accuracy. If not then it shows a manufacturing variance and then you would need to account for that by calibrating to the 35 ppt. instead and not relying only on the RODI calibration. Randy goes through a discussion on offset and slope of the assumed linear calibration relationship. We have control over adjusting the offset but not slope of the linear relationship.

So you should be fine using the Red Sea Refractometer and calibrating to 0 ppt - assuming the "asw" is a salt mix that does a reasonable job simulating natural seawater. Maximum accuracy can be achieved with the additional check at a standard 35 ppt after calibrating at 0 ppt.

Thanks for very detailed reply,much appreciated,think I've read one off these articles but not the other,will have a read over them over next few days so thanks for that.

Was just curious why they kept saying Sea water and nsw,and my paranoid head thought maybe it's a get out clause if got any complaints if found out USER not using nsw ha ha
Anyway thanks once again