Question regarding Refractometer calibration fluid

[beachsidereefer]

Hi Randy,

I consider myself an advanced aquarist but I'm just stumped by 35 PPT calibration fluid. I have three bottles of calibration fluid, two of them brand new, one- brightwell aquatics the other Aquacraft. The third is roughly half empty after using it for a couple months, it's Aquacraft brand.

Aqua Craft Standard Seawater 35 ppt Refractometer Calibration Solution - 60 ml

Brightwell Aquatics Refractometer Calibration Standard, Accurate Reference for The Calibration of Seawater Refractometers, Hydrometers & Other Density

I'm seeing a delta of 4 PPT between the two new bottles, aqua craft vs. brightwell solutions. Same refractometer. solutions and refractometer kept in the same room so they are at equal ambient temp. I'm doing multiple tests and carefully drying off the refractometer after each test. the deviation is consistent after 3-4 tests with each solution

comparing the new aquacraft to the old aquacraft bottle. I see a 1 PPT deviation, I suspect that's because of some degradation from this bottle being used over a couple of months. Might have left the cap off one or twice.

but I'm just stumped as to why I'm seeing such a significant difference between the two new bottles.

finally, am I overthinking this to much, I know I shouldn't chase numbers but I think it's important to stay consistent at 35 PPT so I'm concerned with the variation I'm seeing between calibration solutions.

what do you consider the gold standard for refractometer calibration solution?

appreciate your help and knowledge as always!

Thank you,
Beachsidereefer

 

[Randy Holmes-Farley]

I would not assume that they were made properly.

Both of the companies that you mention lack my confidence.

I've never tested any commercial standards. The gold standard (IMO) is either a very expensive fluid, such as an IAPSO standard seawater

Subsea Technology Exhibitors San Diego

See the full list of subsea technology and ocean engineering exhibitors at Oceanology International Americas, in San Diego.

www.oceanologyinternational.com

or my DIY if you have a good scale

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

 

[beachsidereefer]

I would not assume that they were made properly.

Both of the companies that you mention lack my confidence.

I've never tested any commercial standards. The gold standard (IMO) is either a very expensive fluid, such as an IAPSO standard seawater

Subsea Technology Exhibitors San Diego

See the full list of subsea technology and ocean engineering exhibitors at Oceanology International Americas, in San Diego.

www.oceanologyinternational.com

or my DIY if you have a good scale

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

thank you as always, I have a good quality, digital scale so I'll give your DIY a try! Have a great weekend!

 

[rkpetersen]

FWIW, I've also run into inconsistencies between 3 different commercial salinity standards, not including the 2 already mentioned. It's annoying. Some solutions seem to be made for a specific probe and not necessarily accurate with a refractometer, for example. I've pretty much stopped trying to make everything agree. Stability becomes more important than perfect accuracy. That said, that DIY salinity solution is pretty handy.

 

[beachsidereefer]

I would not assume that they were made properly.

Both of the companies that you mention lack my confidence.

I've never tested any commercial standards. The gold standard (IMO) is either a very expensive fluid, such as an IAPSO standard seawater

Subsea Technology Exhibitors San Diego

See the full list of subsea technology and ocean engineering exhibitors at Oceanology International Americas, in San Diego.

www.oceanologyinternational.com

or my DIY if you have a good scale

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

Hi Randy,

Wanted to circle back to share with you some results. I mixed up a calibration solution using my digital, scientific scale per your formula. Next, I calibrated my refractometer three times using this solution.

I tested each of these solutions, three times, and averaged the results.

starting from the left:
32.0: 3 months old, only used a few times.
33.0: brand new, used a couple of times
36.0: half-empty bottle, 2 month old
35.5 brand new bottle

the lesson learned will be making my own calibration solution using your formula from now on!

 

[infinite0180]

I would not assume that they were made properly.

Both of the companies that you mention lack my confidence.

I've never tested any commercial standards. The gold standard (IMO) is either a very expensive fluid, such as an IAPSO standard seawater

Subsea Technology Exhibitors San Diego

See the full list of subsea technology and ocean engineering exhibitors at Oceanology International Americas, in San Diego.

www.oceanologyinternational.com

or my DIY if you have a good scale

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

randy, is this the salt you used? I just added 3.29g of this plus enough rodi water to make 100g total and test my Hanna conductivity meter. Definitely a discrepancy between this and the Hanna salinity calibration packets. I just tested my tank after using the diy solution i made to calibrate my meter and im at 36.6ppt....

edit -

to further confirm, i made your diy refractometer solution and calibrated my refractometer with it. It reads 36-37ppt... man i wonder how long my salinity has been high...

 

[beachsidereefer]

randy, is this the salt you used? I just added 3.29g of this plus enough rodi water to make 100g total and test my Hanna conductivity meter. Definitely a discrepancy between this and the Hanna salinity calibration packets. I just tested my tank after using the diy solution i made to calibrate my meter and im at 36.6ppt....

edit -

to further confirm, i made your diy refractometer solution and calibrated my refractometer with it. It reads 36-37ppt... man i wonder how long my salinity has been high...

that's the salt I used to make Randy's solution. I found that warming up the RODI water in the microwave helped melt all the salt when mixing it.

 

[infinite0180]

that's the salt I used to make Randy's solution. I found that warming up the RODI water in the microwave helped melt all the salt when mixing it.

Ok good. Yea i actaully did the same thing with the microwave lol

 

[shred5]

Yep I have half a dozen bottles all read different.
I also own a very good refractometer a Vee Gee Scientific refractometer.
I now use a Hanna checker.

 

[Randy Holmes-Farley]

randy, is this the salt you used? I just added 3.29g of this plus enough rodi water to make 100g total and test my Hanna conductivity meter. Definitely a discrepancy between this and the Hanna salinity calibration packets. I just tested my tank after using the diy solution i made to calibrate my meter and im at 36.6ppt....

edit -

to further confirm, i made your diy refractometer solution and calibrated my refractometer with it. It reads 36-37ppt... man i wonder how long my salinity has been high...

The Hannah you mention is a conductivity meter, right? They also make a refractometer.

Did the Hanna packets read high or low after calibrating to the 3.29 solution?

 

[infinite0180]

The Hannah you mention is a conductivity meter, right? They also make a refractometer.

Did the Hanna packets read high or low after calibrating to the 3.29 solution?

Yes it is a conductivity checker. Heres the info on it:

Marine Salinity Tester - HI98319

Hanna Instruments HI98319 Marine Salinity Tester measures conductivity (EC) to determine the salinity of natural and artificial seawater within seconds.

www.hannainst.com

ill have to double check. All i know is last night i calibrated the meter with a fresh Hanna Packet. Then today i stumbled upon this thread and decided to give the diy solution a shot because i recently got a nice little scale. After placing the checker in the diy solution i believe it read low (like 32ish) but i dont remember exactly. Then i cleared the meter and recalibrated with the diy solution. Thats when i checked my tank and saw that i was at 36.7ppt. Did i make the solution correctly by adding 3.29g salt and 96.71g water? I can open a new Hanna packet tonight and see what the meter reads...

 

[Randy Holmes-Farley]

That is the correct recipe for 53 mS/cm or 35 ppt on a conductivity meter.

 

[infinite0180]

That is the correct recipe for 53 mS/cm or 35 ppt on a conductivity meter.

Looks like ill be using this recipe from here on out... thanks Randy

 

[infinite0180]

That is the correct recipe for 53 mS/cm or 35 ppt on a conductivity meter.

Ok Randy,
I decided to open another packet of the Hanna calibration solution. I figured they are all probably junk anyway. So remember, i calibrated the salinity checker earlier with your diy recipe. When i checked the new packed it read 36.5ppt. This makes sense seeing as my tank is reading 36.7ppt, and ive been using the checker to maintain my salinity and make new saltwater. So the checker is meant to be calibrated at 35ppt and instead this whole time its been calibrated at 36.5ppt. Well, at least since i ordered these packets months ago. I usually calibrate this thing monthly. So putting all this evidence together it would appear that my salinity is high. Sometimes its probably been as high as 37ppt. Im going to allow my auto water changer to remove small amounts of water from my sump but not replace it and instead let the ato do its thing. It should take a few days to lower to 35ppt with this method. Just to be sure, i looked everywhere on the salinity checker paperwork and the packet and it does not state 53 ms/cm, it only states 35ppt and to not use the solution to calibrate a refractometer (makes sense). That means its meant to be calibrated with a solution at 53 ms/cm, right? Has to be...

 

[Randy Holmes-Farley]

Ok Randy,
I decided to open another packet of the Hanna calibration solution. I figured they are all probably junk anyway. So remember, i calibrated the salinity checker earlier with your diy recipe. When i checked the new packed it read 36.5ppt. This makes sense seeing as my tank is reading 36.7ppt, and ive been using the checker to maintain my salinity and make new saltwater. So the checker is meant to be calibrated at 35ppt and instead this whole time its been calibrated at 36.5ppt. Well, at least since i ordered these packets months ago. I usually calibrate this thing monthly. So putting all this evidence together it would appear that my salinity is high. Sometimes its probably been as high as 37ppt. Im going to allow my auto water changer to remove small amounts of water from my sump but not replace it and instead let the ato do its thing. It should take a few days to lower to 35ppt with this method. Just to be sure, i looked everywhere on the salinity checker paperwork and the packet and it does not state 53 ms/cm, it only states 35ppt and to not use the solution to calibrate a refractometer (makes sense). That means its meant to be calibrated with a solution at 53 ms/cm, right? Has to be...

It certainly sounds like that is the intent.

Two other possibilities than the Hanna being off is that the salt is moist (try baking it first like a half hour at 350 deg F before weighing it) and see if that changes.

The scale may also be off. Amazon sells cheap calibration weights to check that.

 

[infinite0180]

It certainly sounds like that is the intent.

Two other possibilities than the Hanna being off is that the salt is moist (try baking it first like a half hour at 350 deg F before weighing it) and see if that changes.

The scale may also be off. Amazon sells cheap calibration weights to check that.

Thanks Randy, i purchased a calibration weight with the scale and calibrated it before use. Im fairly confident the scale is accurate enough for this purpose. I will throw some salt in the oven today and see if that changes things!

 

[infinite0180]

It certainly sounds like that is the intent.

Two other possibilities than the Hanna being off is that the salt is moist (try baking it first like a half hour at 350 deg F before weighing it) and see if that changes.

The scale may also be off. Amazon sells cheap calibration weights to check that.

Randy,
Another update. I baked some salt this morning at 350 for a half hour. I recalibrated the scale and made another batch of diy solution. It did indeed change the results, but only slightly at 0.4ppt. The meter calibrated yesterday (with unbaked salt) read 35.4ppt this morning in the fresh batch. So maybe the Hanna packets were closer to only being off by 1ppt - 1.3ppt, but still thats kind of a lot... i checked my tank as well and im down to 35.7ppt but ive been slowly replacing saltwater with rodi water since 2pm yesterday. By tomorrow i should be at 35ppt. Im much more confident in making my own from here on out. Can i store the baked salt in a zip lock baggy for a few months or should i rebake monthly when i calibrate?

Thank you for your help!

 

[Randy Holmes-Farley]

The sealed up solution in a closed container is going to be pretty stable in salinity.

 

[Reefer37]

I would not assume that they were made properly.

Both of the companies that you mention lack my confidence.

I've never tested any commercial standards. The gold standard (IMO) is either a very expensive fluid, such as an IAPSO standard seawater

Subsea Technology Exhibitors San Diego

See the full list of subsea technology and ocean engineering exhibitors at Oceanology International Americas, in San Diego.

www.oceanologyinternational.com

or my DIY if you have a good scale

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

Hey Randy, do you recommend the RODI water be at tank temp before mixing in Morton's? Does it need to mix for a specific period of time? I assume this recipe can be halved or fourths since just needing a small amount of calibration fluid? Not really needing 2 liters worth.

 

[Randy Holmes-Farley]

If it is an ATC (automatic temperature compensation) refractometer, temp should not matter, but room temp to tank temp would be best. I would not want it extra hot or cold.

I have never understood the manufacturer claim that calibration needs to be done at a specific temperature. The ATC is purely mechanical and will compensate for the calibration just the same as for a measurement.

Being as close as possible to tank temp cannot hurt, however, and relieves one of relying on the ATC to be accurate.