Question regarding Refractometer calibration fluid

[Reefer37]

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.

Good to know. How long would you recommend to mix for before testing the salinity?

 

[Randy Holmes-Farley Verified Community Expert]

As soon as it is visibly dissolved and clear it is good to go. If any trace particulates remain, let them settle out.

 

[beachsidereefer]

@Randy Holmes-Farley Hi Randy, the saga continues! I went ahead and invested in a Red Sea Refractometer as understand it's of a higher quality and accuracy than what you find on Amazon. Per the instructions, it says to use RO water to set calirate it to zero so I used RO/DI water that according to the sensor reads 0 TDS.

After calibrating it I put some of the calibration solution I made using your instructions for Refractometer Standard Morton salt and RO/DI water. I have a scientific digital scale and I baked the Morton salt at 350 degrees to make sure it didn't have any moisture so I feel confident I've got a good standard.

so I'm confused that after calibrating the Red Sea refractometer to zero and then taking a measure using the standard solution I mixed. I'm seeing 38 PPT. I even went through the trouble of making sure the RO/DI water, standard solution and refractometer were at the same ambient temp to mitigate that throwing off the calibration.

appreciate any help as I'm pretty much confused at this point!

 

[Randy Holmes-Farley Verified Community Expert]

@Randy Holmes-Farley Hi Randy, the saga continues! I went ahead and invested in a Red Sea Refractometer as understand it's of a higher quality and accuracy than what you find on Amazon. Per the instructions, it says to use RO water to set calirate it to zero so I used RO/DI water that according to the sensor reads 0 TDS.

After calibrating it I put some of the calibration solution I made using your instructions for Refractometer Standard Morton salt and RO/DI water. I have a scientific digital scale and I baked the Morton salt at 350 degrees to make sure it didn't have any moisture so I feel confident I've got a good standard.

so I'm confused that after calibrating the Red Sea refractometer to zero and then taking a measure using the standard solution I mixed. I'm seeing 38 PPT. I even went through the trouble of making sure the RO/DI water, standard solution and refractometer were at the same ambient temp to mitigate that throwing off the calibration.

appreciate any help as I'm pretty much confused at this point!

This refractometer?

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

How much salt in how much water?

How did you measure each?

 

[beachsidereefer]

This refractometer?

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

How much salt in how much water?

How did you measure each?

yes, that's the one.

Using my digital scale I used this formula: 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water . I used RO/DI water

 

[beachsidereefer]

@Randy Holmes-Farley here's the scale I used and I double checked it's calibration using the supplied weights

 

[greetl01]

Now we can't even count on the calibration????? I'm never going to get this tank up and running

 

[Randy Holmes-Farley Verified Community Expert]

yes, that's the one.

Using my digital scale I used this formula: 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water . I used RO/DI water

I'd buy some inexpensive calibration weights from Amazon to verify the scale. If the weights are correct, the refractometer is off.

Amazon has tons of them for not very much:

 

[Randy Holmes-Farley Verified Community Expert]

Now we can't even count on the calibration????? I'm never going to get this tank up and running

Fortunately, our reef tanks are very forgiving with respect to the required salinity.

 

[beachsidereefer]

Now we can't even count on the calibration????? I'm never going to get this tank up and running

I'd buy some inexpensive calibration weights from Amazon to verify the scale. If the weights are correct, the refractometer is off.

Amazon has tons of them for not very much:

thanks, I'm going to mix up a fresh batch of calibration solution just to make sure it's not that. I'm pretty confident the calibration weights supplied are accurate as two are provided and are equal in weight according to the scale.

 

[greetl01]

Fortunately, our reef tanks are very forgiving with respect to the required salinity.

that's great to hear! I literally have a 10 sheet exel file of info and had finally decided I knew enough to not kill animals. Then I saw this SMH

 

[beachsidereefer]

I'd buy some inexpensive calibration weights from Amazon to verify the scale. If the weights are correct, the refractometer is off.

Amazon has tons of them for not very much:

Hi Randy, mystery solved. The Red Sea refractometer is defective. I determined this by mixing up a fresh batch of calibration solution and some pure RO/DI water. I let the red sea refractometer, my Amazon cheapo brine refractometer, and the two solutions equalize to ambient room temperature to minimize any issues with the ATC feature of either refractometer.

For my test, I calibrated both refractometers using RO/DI water to 0 ppt. I did this because this is per the Red Sea instructions on how to calibrate their refractometer. Then I measured the salinity of the calibration solution. Over five test cycles, the Red Sea measured from 33 up to 38 ppt, not a single test registered at 35 PPT.

The cheapo brine was dead-on perfect for each test at 35 PPT.

so I guess the lesson learned is spending 70 bucks on a quality refractometer wasn't money well spent compared to the cheapo unit I bought for like 20 bucks off Amazon.

As always, thank you for all your help and advice!