Calibrating a refractometer with distilled water?

[LordJoshaeus]

Hello everyone! I have been having issues mixing my saltwater to the correct salinity lately and wanted to make sure I am calibrating my refractometer correctly. I have been using distilled water to calibrate the refractometer...does that work, or do I need a known saltwater solution to calibrate it? Thank you :)

 

[Harpo]

The instructions on my VEEGEE refractometer specifically calls for using distilled water for calibration.

 

[Miami Reef]

It’s better to use a seawater standard than RO/DI. It will be more accurate.

Fortunately, a DIY recipe is easy and cheap. Use Morton Ionized salt from the grocery store:

For Refractometer 35ppt standard:

dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified freshwater.

For a rougher measurement in the absence of an accurate water volume or weight measurement:

1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1 teaspoon of salt (making about 79.3 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified freshwater (about 2104.4 g)
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container.

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

 

[Miami Reef]

The instructions on my VEEGEE refractometer specifically calls for using distilled water for calibration.

There are some true seawater refractometers that require distilled water for calibration. For those instruments, RO/DI is fine.

However, for the cheaper, handheld refractometers that are mass produced, those are better with a standard close to 35ppt.

 

[LordJoshaeus]

It’s better to use a seawater standard than RO/DI. It will be more accurate.

Fortunately, a DIY recipe is easy and cheap. Use Morton Ionized salt from the grocery store:

For Refractometer 35ppt standard:

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

Does it have to be ionized salt? I have a lot of canning salt lying around from hatching brine shrimp for my freshwater fish.

 

[DHill6]

The instructions on my VEEGEE refractometer specifically calls for using distilled water for calibration.

Same here. Been using Veegee for years.

 

[Miami Reef]

There are some true seawater refractometers that require distilled water for calibration. For those instruments, RO/DI is fine.

However, for the cheaper, handheld refractometers that are mass produced, those are better with a standard close to 35ppt.

Source:

It is possibly accurate for a true seawater refractometer (assuming it is made correctly), but it is inherently inaccurate for a brine refractometer, which are a large fraction of what type folks get. That is because brine and seawater do not have the same properties. We fix that by calibrating it to seawater 35 pot standard.

Does it have to be ionized salt? I have a lot of canning salt lying around from hatching brine shrimp for my freshwater fish.

I’m not 100% sure. Hopefully Randy will chime in. I think it’s best to use Morton iodized (common household table salt). I think it’s best to use that brand since the recipe was made with it in mind. It’s very inexpensive and has many uses for cooking and seasoning. :)

 

[Fish Fan]

Does it have to be ionized salt? I have a lot of canning salt lying around from hatching brine shrimp for my freshwater fish.

I believe you guys mean salt with Iodine (a common, nutritional additive to table salts), and not ionized salt, just to point it out ;-)

And no, I would in fact suggest using a salt without added iodine, something like Morton's Kosher salt, which is just plain salt, no extra iodine. This is just my gut feeling, but I don't know why you'd want/need iodine in your calibration solution.

EDIT: And my memory of chemistry is a bit fuzzy, but I believe canning salt may be a totally different animal, like sodium nitrate instead of sodium chloride, but I'm not sure. You would almost certainly want sodium chloride (common table salt) for the calibration solution recipe linked above.

 

[BeanAnimal]

There are some true seawater refractometers that require distilled water for calibration. For those instruments, RO/DI is fine.

However, for the cheaper, handheld refractometers that are mass produced, those are better with a standard close to 35ppt.

I would still calibrate with a standard closer to what is being measured.

 

[Fish Fan]

I would still calibrate with a standard closer to what is being measured.

Good point. For most meters that I know of, you want to calibrate it using a standard that close to your expected measurements.

 

[Miami Reef]

I would still calibrate with a standard closer to what is being measured.

Some instruments only allow for freshwater calibration, like the Milwaukee.

You can always double check the accuracy with a seawater standard.

 

[Solo McReefer]

Hello everyone! I have been having issues mixing my saltwater to the correct salinity lately and wanted to make sure I am calibrating my refractometer correctly. I have been using distilled water to calibrate the refractometer...does that work, or do I need a known saltwater solution to calibrate it? Thank you :)

I have bought 3 different calibration 35PPT fluids. From Amazon, within 2 week period

They are all different specific gravities

One had salt crusties on the lid lip when I opened it, obviously leaked and liquid evaporated

I would trust a 35PPT fluid that I made myself, after these discrepancies

Nothing from store now

 

[Solo McReefer]

Some instruments only allow for freshwater calibration, like the Milwaukee.

You can always double check the accuracy with a seawater standard.

Ya

I ran into that problem. That's zeroing

Not really calibration

After I zeroed mine

It caused my 35 PPT calibration fluid to read artificially high

After checking with 2 more commercial calibration fluids, all reading differently

I am taking the Milwaukee zero, as it is. And keeping that as the standard

Steam distilled and my 0TDS RODI zero at the same point. Zeroed with both, then tested with both, resulting zero

I suspect the calibration fluids all are evaporating while on the shelves at Amazon or wherever they are before getting to me

 

[BeanAnimal]

Some instruments only allow for freshwater calibration, like the Milwaukee.

That is a limitation of the firmware and to that end, that device is garbage.

You can always double check the accuracy with a seawater standard.

Certainly, but why not just calibrate to it?

 

[BeanAnimal]

Ya

I ran into that problem. That's zeroing

Not really calibration

After I zeroed mine

It caused my 35 PPT calibration fluid to read artificially high

After checking with 2 more commercial calibration fluids, all reading differently

I am taking the Milwaukee zero, as it is. And keeping that as the standard

Steam distilled and my 0TDS RODI zero at the same point. Zeroed with both, then tested with both, resulting zero

I suspect the calibration fluids all are evaporating while on the shelves at Amazon or wherever they are before getting to me

Buy a floating hydrometer as your standard. The Milwaukee is not reliable as one, if at all.

 

[Solo McReefer]

Buy a floating hydrometer as your standard. The Milwaukee is not reliable as one, if at all.

Yup

I always have a glass hydrometer in every tank(sump really)

The Milwaukee is great for when I am topping off tablespoons of salt while mixing new, sneaking up to match tank SG

I didn't know it couldn't be calibrated when I got it

 

[drolmaeye]

That is a limitation of the firmware and to that end, that device is garbage.

I disagree. I have used the Milwaukee device a fair bit and I would not characterize it as garbage. Moreover, while I certainly understand the argument to calibrate a device close to the target measurement value, I also understand a manufacturer's choice to have a more universal calibration.

 

[Solo McReefer]

Zeroing a measurement device is not calibrating a measurement device

It's so obvious, yet all the Milwaukee documentation egregiously calls it such

 

[BeanAnimal]

Yup

I always have a glass hydrometer in every tank(sump really)

The Milwaukee is great for when I am topping off tablespoons of salt while mixing new, sneaking up to match tank SG

I didn't know it couldn't be calibrated when I got it

I have had two of them. Neither worked worth a hoot.

By floating hydrometer, I mean a large one like the Tropic Marin.

 

[BeanAnimal]

I disagree. I have used the Milwaukee device a fair bit and I would not characterize it as garbage. Moreover, while I certainly understand the argument to calibrate a device close to the target measurement value, I also understand a manufacturer's choice to have a more universal calibration.

You have used it a fair bit, but in reference to what standard? itself?

The argument to calibrate close to the measure is to ensure accurate measurement, there is no need for a “universal” calibration (I assume that is what you mean by calibrating at zero) unless you plan to measure over a wide range. That is the point. The Milwaukee is not a good device, partly for that reason but more so because it is error prone based on ambient light and other issues.