Salinity, Refractor, and Calbration

[oldschoolgoods]

Ok, here’s a tell of a possibly crappy product. The link above says it is 35 ppt and literally on both the label and the advertisement it says it is 53 us/cm. lol

Should be 53 mS/cm.

Having your actual product label (not just an ad typo) off by a factor of 1000 does not inspire any confidence whatsoever.

The bottle I have does say 53 ms/cm. But I do see in the Amazon pic it says us/cm. So that’s weird

 

[Randy Holmes-Farley Verified Community Expert]

I’m using this one. I am willing to upgrade. I see a lot of mixed reviews on digital so I would prefer old school

https://a.co/d/0bmOtdOz

I’d recommend a diy salinity standard for that one.

 

[oldschoolgoods]

I’d recommend a diy salinity standard for that one.

I can understand that. Is there a better refractor you can recommend. It’s not about money it’s about getting everything proper.

 

[Randy Holmes-Farley Verified Community Expert]

I can understand that. Is there a better refractor you can recommend. It’s not about money it’s about getting everything proper.

Which can be done easily with a proper standard. A “better” device is not needed.

Here’s the recipe:

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

Refractometer Standard

It is widely believed that only pure water is required to calibrate refractometers. That fact is true of some refractometers (known as true seawater refractometers; if it doesn’t say it is one, it likely is not), and it may be acceptable for routine calibration, but even for a true seawater refractometer, it assumes that they were manufactured correctly and have not been damaged since manufacturing. As refractometers used by aquarists become less and less expensive due to mass manufacture, there is every reason to believe that at some point they will no longer be accurate enough.

The only way to be sure that a given refractometer gives useful information is to check its accuracy in a solution similar to aquarium water. I believe that all refractometers should be calibrated or at least checked in this fashion when first purchased, and again any time there is a reason to be concerned. For example, an aquarist might be concerned if an aquarium that had been running for years at a salinity of 35 ppt suddenly reads 39 ppt.

In order to provide a standard for refractometers, a solution whose refractive index is similar to normal seawater is required. Seawater with S= 35 has a refractive index of 1.3394.1 Likewise, the refractive index of different sodium chloride solutions can be found in the scientific literature. My CRC Handbook of Chemistry and Physics (57th Edition, Page D-252)4 has such a table. That table has entries for 3.6 and 3.7 weight percent solutions of sodium chloride that span the value for normal seawater. Interpolating between these data points suggests that a solution of 3.65 weight percent sodium chloride has the same refractive index as S=35 seawater, and can be used as an appropriate standard(Table 2).

This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water. That amount roughly corresponds to ¼ cup (73.1 g) of Morton's Iodized Salt dissolved into 2 liters (2000 g) of water (giving very slightly more than 2 L of total volume).

 

[oldschoolgoods]

Which can be done easily with a proper standard. A “better” device is not needed.

Here’s the recipe:

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

Refractometer Standard

It is widely believed that only pure water is required to calibrate refractometers. That fact is true of some refractometers (known as true seawater refractometers; if it doesn’t say it is one, it likely is not), and it may be acceptable for routine calibration, but even for a true seawater refractometer, it assumes that they were manufactured correctly and have not been damaged since manufacturing. As refractometers used by aquarists become less and less expensive due to mass manufacture, there is every reason to believe that at some point they will no longer be accurate enough.

The only way to be sure that a given refractometer gives useful information is to check its accuracy in a solution similar to aquarium water. I believe that all refractometers should be calibrated or at least checked in this fashion when first purchased, and again any time there is a reason to be concerned. For example, an aquarist might be concerned if an aquarium that had been running for years at a salinity of 35 ppt suddenly reads 39 ppt.

In order to provide a standard for refractometers, a solution whose refractive index is similar to normal seawater is required. Seawater with S= 35 has a refractive index of 1.3394.1 Likewise, the refractive index of different sodium chloride solutions can be found in the scientific literature. My CRC Handbook of Chemistry and Physics (57th Edition, Page D-252)4 has such a table. That table has entries for 3.6 and 3.7 weight percent solutions of sodium chloride that span the value for normal seawater. Interpolating between these data points suggests that a solution of 3.65 weight percent sodium chloride has the same refractive index as S=35 seawater, and can be used as an appropriate standard(Table 2).

This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water. That amount roughly corresponds to ¼ cup (73.1 g) of Morton's Iodized Salt dissolved into 2 liters (2000 g) of water (giving very slightly more than 2 L of total volume).

Which can be done easily with a proper standard. A “better” device is not needed.

Here’s the recipe:

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

Refractometer Standard

It is widely believed that only pure water is required to calibrate refractometers. That fact is true of some refractometers (known as true seawater refractometers; if it doesn’t say it is one, it likely is not), and it may be acceptable for routine calibration, but even for a true seawater refractometer, it assumes that they were manufactured correctly and have not been damaged since manufacturing. As refractometers used by aquarists become less and less expensive due to mass manufacture, there is every reason to believe that at some point they will no longer be accurate enough.

The only way to be sure that a given refractometer gives useful information is to check its accuracy in a solution similar to aquarium water. I believe that all refractometers should be calibrated or at least checked in this fashion when first purchased, and again any time there is a reason to be concerned. For example, an aquarist might be concerned if an aquarium that had been running for years at a salinity of 35 ppt suddenly reads 39 ppt.

In order to provide a standard for refractometers, a solution whose refractive index is similar to normal seawater is required. Seawater with S= 35 has a refractive index of 1.3394.1 Likewise, the refractive index of different sodium chloride solutions can be found in the scientific literature. My CRC Handbook of Chemistry and Physics (57th Edition, Page D-252)4 has such a table. That table has entries for 3.6 and 3.7 weight percent solutions of sodium chloride that span the value for normal seawater. Interpolating between these data points suggests that a solution of 3.65 weight percent sodium chloride has the same refractive index as S=35 seawater, and can be used as an appropriate standard(Table 2).

This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water. That amount roughly corresponds to ¼ cup (73.1 g) of Morton's Iodized Salt dissolved into 2 liters (2000 g) of water (giving very slightly more than 2 L of total volume).

I am going to have to try to make that solution to check things out in the long run for peace of mind. In the mean time since I am not 100% comfortable making that. I purchased a Vee Gee STX-3 refractor and carefully calibrated it following instructions with distilled water at 68 degrees. It said my salinity was 1.022. I tested the water from one of the stores I mentioned before that came in high on my other refractor. This time it came in at 1.025 on the Vee Gee. So then I tested the 35ppm solution and it came in at 1.021. I am leaving a review for the solution and returning it. Now I get to slowly work on getting my aquarium to 1.026 now. Lesson learned.

 

[oldschoolgoods]

Not to mention the Vee Gee feels like a tool. It’s heavy and solid. The Amazon refractor was so light and felt cheep in hand. I feel I made a good choice.

 

[bandando]

When I bought the TM hydrometer I eliminate every other instrument for checking the salinity in my tank.

 

[Seregus]

Of cource its personal thing to do so, but having redundancy in measurement tools to validate results and have a backup option in case something gets broken is always a good option, in my opinion? Also if you have 3-4 different type of measurements and they all show same result you are more likely to actually have it as they all show.

 

[Randy Holmes-Farley Verified Community Expert]

When I bought the TM hydrometer I eliminate every other instrument for checking the salinity in my tank.

I have nothing against the TM hydrometer, assuming that folks check it once to be sure it was actually made correctly.

My biggest knock on it is the substantial inconvenience of measuring salinity that way, relative to dropping a quality conductivity probe in the water.

 

[oldschoolgoods]

I have nothing against the TM hydrometer, assuming that folks check it once to be sure it was actually made correctly.

My biggest knock on it is the substantial inconvenience of measuring salinity that way, relative to dropping a quality conductivity probe in the water.

You seem very verse and intelligent on everything in this hobby. What’s your feelings on the Vee Gee? Is it as good as what I’ve read? Should I get a TM hydrometer as a 2nd source

 

[Randy Holmes-Farley Verified Community Expert]

Thanks!

The Vee Gee is a fine device. Just be sure to calibrate it reasonably frequently (see if it drifts, if not, calibrate less and less frequently) and at least once, test it with a good quality 35 ppt standard.

Folks like the fact that the TM hydrometer never needs calibration. But it is fairly inconvenient to use. It's a fine device.

I personally use conductivity for salinity measurement.

 

[get-salty]

When starting my aquarium I read here I was suppose to calibrate my refractor with a 35PPM solution not RO or distilled and that’s what did. I used Reagents Solution. My tank is thriving and everything is growing and looks happy n healthy. Anyways recently I’ve tested the water in my bags of fish and corals from both stores I frequent. One was 1.030 and the other I believe was 1.028 (I can’t recall to the exact point as I didn’t make a note of that one and it was a little while ago). When I did a test calibration with RO before my solution came mine was about 1.028. I assume I’m doing right calibrating with the solution and I should ignore the stores higher numbers? Mine is coming is at 1.026

I have test solution and tbh both solution and RO gives same results.. at least on my refractometer. Will i be buying another bottle of test solution? Absolutely, they are cheap and ill use it for comparison

 

[jabberkaycee]

I calibrated my refractor with RO water to zero, then verified with calibration fluid, which was spot on.

 

[exnisstech]

I used to use Randy's calibration fluid and refractometers but switched to a TM hydrometer. It's not the quickest to use but i find it less hassle than having to check calibration all the time. I use the hydrometer at my mixing station and I picked up a pinpoint tester to spot check tanks. I still have the refractometers and even my cheap ATO one from Amazon still works fine after 10 years.