High Quality Refractometer Recommendations?

[diverjm]

Well, it sounds like myself and countless others have made errors or have a wide range of accuracy criteria to think that this piece of equipment actually functions as it should. Same goes for the ICP tests that align with the readings.

 

[slingfox]

I do not see it making any such claim, and thus I would expect it is not.

Handheld Salinity Refractometer

Order your Handheld Salinity Refractometer online today with VEE GEE Scientific and receive free shipping and fast delivery.

www.veegee.com

Are there any saltwater refractometers that hobbiest can purchase?

 

[Randy Holmes-Farley]

Are there any saltwater refractometers that hobbiest can purchase?

Sure. I'm not necessarily making a brand recommendation, but these are seawater refractometers (or at least claim to be)

D-D True Seawater Refractometer​

Red Sea Seawater Refractometer

Milwaukee MA887 Digital Refractometer Seawater

HANNA instruments hi96822 Seawater Salinity Refractometer

 

[2Barrel]

As others have posted. The VEE GEE STX-3 is excellent.
Spot on with my Tropic Marin glass hydrometer.

 

[Aspect]

Doesn't the fact that 35 ppt aligns with 1.0264 on its viewing scale suggest that it is a seawater refractometer?

No that's just normal conversion every refractometer will align like that

 

[RobertK]

No that's just normal conversion every refractometer will align like that

No, my old refractometer had 35 ppm aligned with 1.025 and Randy told me that was because it was not a seawater refractometer. Perhaps I was incorrect in therefore assuming that the different scale on the VeeGee meant that it is a seawater refractometer.

 

[BriDroid]

I got 3 Reefractometers from Marine and Reef as gifts when I bought my Kessil pendants. I have to say that I’m really impressed with them. They’re much shorter than standard refractometers and they have a 0-40ppt scale instead of the 0-100ppt scale. It’s easier to read for me. They all hold a calibration really well too using Randy’s DIY solution. It’s nice to get something useful for “free” (not really free with the $$ I dropped)

 

[Aspect]

No, my old refractometer had 35 ppm aligned with 1.025 and Randy told me that was because it was not a seawater refractometer. Perhaps I was incorrect in therefore assuming that the different scale on the VeeGee meant that it is a seawater refractometer.

That was either an eyesight error or a chart manufacturing error on the refractometer. 35 ppt always = 1.0264 sg it's just a conversion

 

[Randy Holmes-Farley]

That was either an eyesight error or a chart manufacturing error on the refractometer. 35 ppt always = 1.0264 sg it's just a conversion

That's true for seawater, but not a brine refractometer, and if one can see the markings precisely enough, its one way to know which type it is.



Refractometers and Salinity Measurement

from it:

Imperfect Refractometer Use: Scale Misunderstanding and Salt Refractometers

Refractometers can lead to incorrect readings in additional ways and, again, these issues abound for reef aquarists. One is that many refractometers are intended to measure sodium chloride solutions, not seawater. These are often called salt or brine refractometers. Despite the scale reading in ppt (‰) or specific gravity, they are not intended to be used for seawater. Unfortunately, many refractometers used by aquarists fall into this category. In fact, very few refractometers used by hobbyists are true seawater refractometers. If a manufacturer does not claim it is a “True Seawater” refractometer, it very likely is a brine refractometer.

Fortunately for aquarists, the differences between a salt refractometer and a seawater refractometer are not too large. A 35 ppt sodium chloride solution (3.5 weight percent sodium chloride in water) has the same refractive index as a 33.3 ppt seawater solution, so the error in using a perfectly calibrated salt refractometer is about 1.7 ppt, or 5% of the total salinity. This error is significant, in my opinion, but not usually enough to cause a reef aquarium to fail, assuming the aquarist has targeted an appropriate salinity in the first place. Figure 23 shows the relationship between a perfectly calibrated and accurate salt refractometer and a perfectly calibrated and accurate seawater refractometer when the units are reported in salinity. This figure shows the measured salinity reading for seawater being about 1.7 ppt higher than it really is.


Figure 23. The relationship between the real (actual) salinity and the measured salinity (in ppt) for a perfectly calibrated seawater refractometer (green) and a perfectly calibrated salt refractometer (red). This salt refractometer effectively has a significant slope error, with values far from the calibration point (freshwater with a salinity of 0 ppt) reading roughly 1.7 ppt higher than the actual value. Salt refractometers reading in salinity can be recalibrated using seawater to eliminate nearly all of this error (just as the refractometer in Figures 17 and 18 was recalibrated in seawater to give Figures 21 and 22).

It turns out that this is a slope miscalibration in the sense that a perfectly made sodium chloride refractometer necessarily has a different relationship between refractive index and salinity than does seawater. This type of problem with a refractometer IS NOT at all corrected by calibrating it with pure freshwater. If you have this type of refractometer, and it was perfectly made and calibrated in freshwater, it will ALWAYS read seawater to be higher in salinity than it actually is (misreporting an actual 33.3 ppt to be 35 ppt).

Even more confusing, but perhaps a bit less of a problem in terms of the error’s magnitude, salt refractometers sometimes read in specific gravity. But that value is specific gravity of a sodium chloride solution with the measured refractive index, not seawater with that refractive index. A sodium chloride solution with the same refractive index as 35 ppt seawater (which turns out to be 36.5 ppt sodium chloride) has a specific gravity matching 34.3 ppt seawater. So this type of refractometer, when perfectly calibrated, will read the specific gravity of 35 ppt seawater to be a bit low, at 1.0261 instead of about 1.0264. That error (reading 0.0003 or so too low) is, however, probably less than most reef aquarists are concerned with. Figure 24 shows the relationship between a perfectly calibrated and accurate salt refractometer and a perfectly calibrated and accurate seawater refractometer when the units are reported in specific gravity. This figure shows the measured salinity reading for seawater being about 0.0003 lower than it really is.


Figure 24. The relationship between the real (actual) specific gravity and the measured specific gravity for a perfectly calibrated seawater refractometer (green) and a perfectly calibrated salt refractometer (red). This salt refractometer effectively has a very small slope error, with values far from the calibration point (freshwater with a salinity of 0 ppt) reading roughly 0.0003 specific gravity units lower than the actual value. Salt refractometers reading in specific gravity can be recalibrated using seawater to eliminate nearly all of this already small error (just as the refractometer in Figures 15 and 16 was recalibrated in seawater to give Figures 19 and 20).

Regardless of a salt refractometer’s scale reading (ppt or specific gravity), aquarists can get around this problem by calibrating this type of refractometer in a seawater standard (see below). Because that type of calibration also gets around important manufacturing errors (slope calibration defects due to the scale being the wrong dimensions), it solves both problems at once (however, certain digital refractometers such as the Milwaukee can only be calibrated with pure fresh water. That requirement is OK in the Milwaukee case, since it is a “True Seawater” refractometer).

 

[reefmaster70]

Milwaukee MA887 Digital Refractometer Seawater
Is what I use and check it against my Pinpoint digital salinity meter and they are both always spot on. So much better than any manual refractometer.

 

[Aspect]

Yeah gonna go for the Milwaukee digital refractometer and send this veegee back. Tried calibrating it again and leaving it in same room so temp would stay consistent with the temp of the refractometer and it still isn't holding calibration. Also the calibration screw is already stripping after about 4 cycles of tightening/loosening. Honestly thought for how expensive it is they really went super cheap on the included screwdriver.

 

[BeanAnimal]

VeeGee STX-3 is very accurate and lines up with my periodic ICP. I check calibration every six months and not once during the last two years have I had to make any adjustment.

I have tried the cheaper refractometer sold by one of the major online reeding retailers as wells three Hanna salinity checkers. None of those were reliable.

FWIW — ICP does not test salinity. They are using a refractometer, hydrometer or conductivity meter, just like the rest of us.

 

[BeanAnimal]

Milwaukee MA887 Digital Refractometer Seawater

I have had two. Both are in the garbage. They IMHO are toys, not instruments.

 

[Aspect]

I have had two. Both are in the garbage. They IMHO are toys, not instruments.

Why do you say that?

 

[BeanAnimal]

As for the VeeGee — I would venture to say that most of the price is marketing, with the units coming off the same line as many less expensive brands. I had a few and couldn’t tell a difference between them and 3 other brands. There are a few makes that are pure junk, but even those are hard to identify in the mix. The whole hobby refractometer market is cheap China imports.

 

[BeanAnimal]

Why do you say that?

Because they are garbage.
The +/-2 PSU spec on the Milwaukee MA877 is the best case accuracy under ideal conditions with a perfect calibration. Real world will be statistically worse due to user induced variables.

This is for a single measurement and calibration.

However, when you compare two measurements taken on different days with independent calibrations, each reading carries its own error, these may cancel or may stack. So a real 35 PSU over numerous “perfect” calibrated measurements could range from 33 PSU to 37 PSU. Add back in statistical error from sample temperature deviation, room light, standard differences, etc, and that easily becomes 31 PSU to 39 PSU.

This is without getting into display rounding and how that does or does not come into play.

They are toys dressed up as lab instruments.

 

[diverjm]

Okay… so in your opinion, all of the refractometers mentioned including ICP testing is garbage yet you don’t mention what is superior?? How is this helpful to anyone?

 

[slingfox]

FWIW — ICP does not test salinity. They are using a refractometer, hydrometer or conductivity meter, just like the rest of us.

Yup, but good to have another outside source to check the measurement against. In the last year I have done ICPs with ATI, ReefLab, and Fauna Marin and all salinity measurements lined up with the VeeGee. I have a bunch of Modern Reef ICP-MS sitting around but won’t use it until after my upcoming tank swap.

 

[BeanAnimal]

Okay… so in your opinion, all of the refractometers mentioned including ICP testing is garbage.

That is not what I said.

 

[Subsea]

Hello, I'm looking for a refractometer that will hold calibration for longer than a couple days, does anyone have any recommendations? Thank you

If you want a real instrument, then get a multi volt meter and use conductivity readings.

“Conductivity meters (conductivity testers) and refractometers are both used to measure salinity, but they function differently:
conductivity meters measure electricity flow (affected by ion concentration), while refractometers measure the bending of light (refractive index). Conductivity meters are generally faster and more precise, whereas refractometers are often considered more robust for high-concentration salinity without dilution. “

humble.fish +4
Conductivity Meters (Electrical Conductivity/EC)