Salinity Calibration solution issues

Myka · Nov 22, 2016

So, I'm wondering about this...

I have 2 bottles of Pinpoint Seawater Solution. My refractometer measures on of them dead on 35 ppt, the other one is 35 and a hair. A bottle of Two little Fishies AccuraSea solution reads 37 ppt, a second bottle of TLF also reads 37 ppt.

What's going on? Which should I trust? How do I figure out which one is correct?

jason2459 · Nov 22, 2016

https://www.reef2reef.com/threads/does-your-calibration-solution-need-calibrated.250133/

Randy Holmes-Farley · Nov 22, 2016

You have to be careful with calibration fluids that they are intended, or at least suitable, for the device type.

A conductivity standard equivalent to 35 ppt seawater is not necessarily suitable for 35 ppt on a refractometer, depending on how it is made.

The Pinpoint fluid should read 35 ppt on both a refractometer and conductivity meter.

Myka · Nov 22, 2016

Randy Holmes-Farley said:
You have to be careful with calibration fluids that they are intended, or at least suitable, for the device type.

A conductivity standard equivalent to 35 ppt seawater is not necessarily suitable for 35 ppt on a refractometer, depending on how it is made.

The Pinpoint fluid should read 35 ppt on both a refractometer and conductivity meter.

Yes, absolutely. I am not using a conductivity meter, just a refractometer.

I emailed Julian, here's his response:

"AccuraSea reference solution is made from real seawater collected from the sea off Miami Florida. It is the same water we sell as AccuraSea NSW, except that we dilute the reference solution slightly to achieve an exact 35 ppt.
Why dilute it? Because when it is collected from the sea here the salinity is slightly HIGHER than the standard 35 ppt. The standard of 35 ppt is used by Oceanographers as a reference because it has traditionally been the standard at which various values for seawater have been measured and published. [...] We know our reference is correct because we bring a sample from each batch to the University of Miami to verify the reading."

jason2459 said:
https://www.reef2reef.com/threads/does-your-calibration-solution-need-calibrated.250133/

Awesome, thanks Jason!

Myka · Nov 26, 2016

Natural seawater is indeed suitable for calibrating a refractometer, correct?

I just don't understand the big difference.

Randy Holmes-Farley · Nov 26, 2016

Yes, that will be fine.

Not sure why there is a difference.

jason2459 · Nov 26, 2016

IME from personally testing quite frequently (a couple decades ago now) off the coasts of Florida (bay side, gulf, intercoastal, glades, ocean , tidal areas, gulf stream, etc) the salinity fluctuates seasonally to daily near shore.

Usually though salinity levels were lower not high except in very near shore tidal pool like locations. So, not sure why they stated they have to always lower the salinity levels. Get out to the Gulfstream and its pretty even year round. I'm curious where they collect and how its treated afterward.

Here's a good paper showing fluctuaions seasonally and with weather events in the bay side.

Salinity patterns of Florida Bay - National Oceanic and Atmospheric Administration
https://www.google.com/url?sa=t&sou...0TTBw26EK9IMJADwg&sig2=nn6kc3SiAnJltN5yckLJVw