Refractometers And Salinity Measurement

[Randy Holmes-Farley]

Refractometers And Salinity Measurement

Salinity is one of the most important parameters measured in reef aquaria. It controls not only the salt balance between an organism and its surrounding environment, but also the levels of a host of ions in seawater that aquarists neither measure nor control independently. Consequently, aquarists must monitor salinity to ensure that organisms are not stressed by moving between aquaria of potentially different salinity, and that the salinity of the aquarium...

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[Myka]

Hi Randy,

I read almost the entire article. Thank you for such detailed information. I'm looking for a bit of clarity for my particular needs if you don't mind.

I have a refractometer that I've had for about 15 years. It has no markings or brandings on it. It is longer than say a Vertex refractometer if that means anything. It is in a case with instructions for a Link brine refractometer, but the pictures of the scale in the instructions shows a Brix scale. I'm thinking these are not the correct instructions for this refractometer.

This is what my refractometer's scale looks like exactly (inc all markings/numbers/words):

I'm using Sybon Standard Seawater Saline (35ppt/psu, 53.1mS/cm, 77˚F/25˚C) NIST Standard which I replace once a year. You can see here if so desired: https://premiumaquatics.com/products/standard-seawater-saline-35ppt-531mscm77f25c.html

Am I on the right track? With this solution I calibrate my (assumed brine) refractometer to 35 ppt, right? Not 33.3 ppt.

Also, one last thing. I operate an aquarium maintenance company and my refractometer travels a lot of km. I keep it in the vehicle with me, and it spends the nights indoors. It does get exposed to ambient temperatures between -40C to 40C as the vehicle either warms up or cools down between clients. I calibrate it once a week, and find in the summer months it rarely varies, and in cooler months it may walk around 1 ppt or so in between calibration. I've been looking at the Pinpoint Salinity Monitor. Am I better off "abusing" my refractometer as I do, or would a Pinpoint Salinity Monitor be a better choice? How about for my home reef?

Thank you for your time Randy.

 

[Randy Holmes-Farley]

The picture is not a Brix refractometer. The scale 0/00 is ppt. I'd use a seawater standard, calibrate that part to 35, and then only use the right side of the scale and you're good to go!

The inside of your car gets down to -40 deg C? Wow, you live in a cold climate!

If you are comfortable with frequent recalibration, it should be fine, but so is the Pinpoint.

 

[Frop]

The picture is not a Brix refractometer. The scale 0/00 is ppt. I'd use a seawater standard, calibrate that part to 35, and then only use the right side of the scale and you're good to go!

The inside of your car gets down to -40 deg C? Wow, you live in a cold climate!

If you are comfortable with frequent recalibration, it should be fine, but so is the Pinpoint.

I just bought a refractometer. Is it acceptable to zero the gage with RO DI water?

I put the RO DI water on my scale and it reads about 1.002 I tried to clean everything to make sure it wasn't any left over salt. I didn't know if that is an issue. It's the difference from my tank reading 1.025 or 1.023 ;p

 

[Randy Holmes-Farley]

I just bought a refractometer. Is it acceptable to zero the gage with RO DI water?

I put the RO DI water on my scale and it reads about 1.002 I tried to clean everything to make sure it wasn't any left over salt. I didn't know if that is an issue. It's the difference from my tank reading 1.025 or 1.023 ;p

THe proper way to calibrate depends on the type of refractometer, but unless it is and says it is a true seawater refractometer, calibration with Ro/DI won't be perfect with Ro/DI. It may be "adequate" (since exact salinity is not critical) but it is not optimal, even if it is made and calibrated perfectly (which may not be the case for all brands). Calibration with a 35 ppt seawater standard will always give the correct calibration for measuring seawater.

 

[Myka]

The picture is not a Brix refractometer. The scale 0/00 is ppt. I'd use a seawater standard, calibrate that part to 35, and then only use the right side of the scale and you're good to go!

The inside of your car gets down to -40 deg C? Wow, you live in a cold climate!

If you are comfortable with frequent recalibration, it should be fine, but so is the Pinpoint.

Yes the scale on the refractometer is not a Brix scale, but the instructions in the refractometer case are for a Brix refractometer. They must have been mixed up along the way. I hesitate to replace this old refractometer because the scale is much easier to read than most of the cheap hobbyist refractometer available these days.

Yes, it does occasionally get to -40C, though usually "only" -35C. I don't mind calibrating often - it seems once a week is sufficient.

Thanks for your help! I know the part of the article I need to re-read now.

 

[Randy Holmes-Farley]

You're welcome.

Keep Warm!

 

[CJBuckeyes]

Great article Randy !

I've never been able to figure out Redsea's salinity chart. The salinity is relatively higher than the SG than I've seen everywhere else, 35.5/1.0255 as opposed to 35/1.0264 (both at 77 degrees). You mention in the article that Mg can affect this relationship, but that doesn't seem to be the case here. Any idea what might be driving this?

 

[jeff williams]

Randy thanks for clearing up the confusion. I couldn't figure out why my Refractometer calibrated with 35 ppt solution would read below 0 when I put Ro in it. Know I now I have a brine Refractometer not a true saltwater.

 

[Randy Holmes-Farley]

Randy thanks for clearing up the confusion. I couldn't figure out why my Refractometer calibrated with 35 ppt solution would read below 0 when I put Ro in it. Know I now I have a brine Refractometer not a true saltwater.

You're welcome.

Happy Reefing.

 

[Randy Holmes-Farley]

Great article Randy !

I've never been able to figure out Redsea's salinity chart. The salinity is relatively higher than the SG than I've seen everywhere else, 35.5/1.0255 as opposed to 35/1.0264 (both at 77 degrees). You mention in the article that Mg can affect this relationship, but that doesn't seem to be the case here. Any idea what might be driving this?

They certainly seem to not have the correct relationship between the salinity in the table and the specific gravity in the table.

Maybe they do not actually intend them to correspond (which would be strange) or maybe they just got the conversion wrong. Maybe they used density numbers instead of specific gravity.

 

[jeff williams]

Refractometers And Salinity Measurement



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Randy great article was wondering if you could answer this I calibrate my Refractometer with calibration fluid , it is a atc model and I can take a sample of water let it sit 30 sec to a min to acclimate read it clean it off and next time I use it it will be out of calibration. I calibrate it at room temp and store it in the same room as its used. And it is a brine / saltwater Refractometer. Any suggestions

 

[Randy Holmes-Farley]

Many people find their refractometers do not hold calibration. Not sure why, but temperature changes or vibrations may cause minor shifting of the crystal in its holder.

 

[Insane320]

Many people find their refractometers do not hold calibration. Not sure why, but temperature changes or vibrations may cause minor shifting of the crystal in its holder.

What do you think of the electronic Milwaukee??

good points
and the
Bad points[/QUOTE]

 

[Randy Holmes-Farley]

What do you think of the electronic Milwaukee??

good points
and the
Bad points

In principle it is a good product, but some folks do not get the answer i'd expect from it. Not sure why.

For example:

https://www.reef2reef.com/threads/c...ed-lab-grade-units.327201/page-4#post-4134460