Salinity - what to trust?

[xradikalx]

Hey all, thanks for your wisdom!

My question relates to what salinity to trust.

I have a few ways that I check salinity -

1 - A good old fashioned refractometer. I use brightwell standard 35ppm/1.026 sg calibration solution weekly. With this my salinity reads 35

2 - Apex salinity probe. Calibrated using the standard solutions when I installed the unit, about 6 months ago. With this, salinity reads 35 (+/- .2 throughout the day)

3 - I recently sent for a send-out ATI ICP-MS water test. I would think this would be the 'gold standard', however it read my salinity at 33

Which one do I trust? Do I need to recalibrate the apex? Or slowly bring the apex salinity to something like 37?

Thanks!

 

[gbroadbridge]

Hey all, thanks for your wisdom!

My question relates to what salinity to trust.

I have a few ways that I check salinity -

1 - A good old fashioned refractometer. I use brightwell standard 35ppm/1.026 sg calibration solution weekly. With this my salinity reads 35

2 - Apex salinity probe. Calibrated using the standard solutions when I installed the unit, about 6 months ago. With this, salinity reads 35 (+/- .2 throughout the day)

3 - I recently sent for a send-out ATI ICP-MS water test. I would think this would be the 'gold standard', however it read my salinity at 33

Which one do I trust? Do I need to recalibrate the apex? Or slowly bring the apex salinity to something like 37?

Thanks!

Of the three, I would most trust a refractometer calibrated with a DIY calibration solution just before use.

EC testers such as the Apex probe are fine, but tend to drift as crud builds up on the probe.

ICP itself does not directly measure salinity, they are using some other method which often is not disclosed.

 

[edd59]

now i use a hydrometer. when i got it i calibrated my refrac with 35ppt then checked salt sample and they were differant but i feel the hydrometer is more dependable. so thats what i depend on. still use refrac when mixing salt to get in the ball park then use hyd cause hyd is a pain.

 

[WhatCouldGoWrong71]

I use the TM hydrometer. I have a draw full of crap that is never correct. I have a hard timing seeing a refractometer though.

 

[cet98]

In all honesty, the more important aspect of salinity (as is with most aspects of this hobby) is consistency.
A quality refractometer, calibrated properly is more than adequate.
Keeping the salinity reading consistent is your true goal.
Best of luck.

 

[Randy Holmes-Farley]

I would drop the commercial fluid and make diy standards if you have a scale.

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[Fritz05]

I also use the Tropic Marin hydrometer, it does not need calibration, and is always exact.

 

[The Warelock]

I also use the Tropic Marin hydrometer, it does not need calibration, and is always exact.

Need to adjust the hydrometer reading for temperature though, if not measuring exactly 77F water. And maybe however long the hydrometer needs to be in the water to warm the glass if a factor too? And by that time has the water temp changed from sitting in whatever container you’re using? And don’t forget to rinse it in RODI or vinegar or something to make sure there are no deposits left on it. And spin it in the water to make sure no bubbles on it. And don’t break it because it’s the most fragile thing created by mankind. But at least you don’t have to question the validity of refractometer calibration fluid :)

 

[Randy Holmes-Farley]

I recommend checking any hydrometer with a calibration fluid at least once, unless it is an expensive NIST traceable hydrometer. Otherwise, you are assuming that a mass production facility somewhere in the world is making every inexpensive hydrometer perfectly.