Xplain, PPT to SRG no way to convert apples to apples ?

[Val Shebeko]

Yes even converting the numbers does not take into account that they get there measurements differently
That is why we said this right up front:
The Apex probe measures the conductivity of the water, the refractometer measures the change in the speed of light when it goes from air to water, a hydrometer measures how dense the water is. These are 3 different things you are measuring, none of them is a count of the particles of stuff in a million particles of water. All 3 will give different readings if you dissolve different things, 35.0 ppm of sodium chloride will read different than sea water with 35.0 ppm of stuff in a refractometer.
.6 is not that much of a change in the big scope of things. Remember it is all about trends, not specific numbers.

 

[Terence]

Thank you. This is one of the most misunderstood things in reef keeping.
It is a shame really that, because hydrometers were the go-to device early on, everyone gots stuck on a SG number - and it won't leave us. It is like Imperial vs. Metric except they don't directly convert!

 

[Val Shebeko]

So this is complete and utter nonsense ?

https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php

 

[Terence]

It is close, but the best way to understand more about salt is to listen to this podcast featuring Craig Bingman: http://www.reefthreads.com/reef-threads-podcast-245/

 

[beaslbob]

depends on temperature from what I understand.

Which sometimes isn't much. LOL

 

[Terence]

Temp is part of it, and it can make a difference for sure - especially when our customers are looking at a sight-glass and seeing 34.85 (trust me, some think they see that much precision) and then compare it to their Apex which says its 35.1 and then it becomes "The Apex is wrong".

Also, some people use refractometers scaled for salinity, not seawater. Another thing of issue. Also, most people do not calibrate a refractometer correctly - they will tell you it is calibrated - "I just did it with RODI" or "I just calibrated it last week" and in the meanwhile it was dropped onto the table at some point.

There is so much here - and I don't blame people, it is a lot of work and reading to digest - Here is a great write up by RHF on all things salinity that every reefkeeper should read, and then read again.

http://reefkeeping.com/issues/2006-12/rhf/

 

[Randy Holmes-Farley]

The Apex probe measures the conductivity of the water, the refractometer measures the change in the speed of light when it goes from air to water, a hydrometer measures how dense the water is. These are 3 different things you are measuring, none of them is a count of the particles of stuff in a million particles of water. All 3 will give different readings if you dissolve different things, 35.0 ppm of sodium chloride will read different than sea water with 35.0 ppm of stuff in a refractometer.

That is certainly true. That's why my sodium chloride standard for 35 ppt equivalent on each of those devices is slightly different:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-06/rhf/index.htm

35 PSU (ppt) seawater =
3.65 weight percent sodium chloride for refractometers
3.714 weight percent sodium chloride for hydrometers
3.29 weight percent sodium chloride for conductivity

 

[Randy Holmes-Farley]

So this is complete and utter nonsense ?

https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php

While I cannot verify its accuracy, there is nothing inherently wrong with a calculator or conversion table for seawater values.

 

[Val Shebeko]

Informative.

Ordered up a True Sine supposedly designed for testing sea water. We'll see.

 

[Val Shebeko]

When all are properly calibrated for seawater, there will be no difference in the salinity of seawater determined by hydrometer, refractometer, or conductivity meter.

If you get a big difference, something is wrong. A possible culprit is temperature. A conductivity probe must know the temperature to properly calibrate, and if you use something like the Apex where the temp probe remains in the water, it will give incorrect calibration.

 

[Terence]

The Apex has temperature compensation if there is a properly configured conductivity port.

 

[Val Shebeko]

Tell me more about this temp. and Apex.

Did you mean the cal. fluid at room temp confuses the Apex?

 

[Val Shebeko]

Something is screwy here. I have some Apex cal fluid on order and I have ordered up a refrectometer called True Sine which supposed is designed to measure seawater not brine.

It is going to have to be pretty close between the two.

 

[Terence]

Just follow the proscribed processes in the get started instructions. Then you can do temp compensation through a an advanced setting.

No matter what, if your expectation is that you will get all of those devices to align to the 0.1 you are setting yourself up for disappointment and you are frankly wasting your time. Get it close. Look at your tank. Doing good? Great. Keep it in that salinity range +/- .2 on whatever you are reading it on and you will be good.

 

[Val Shebeko]

Well, we will go thru all the steps and see how far they are apart.

Right now the water id being muddied by side issues. We will calibrate the Apex, set the tempurature in advanced settings and see how that compares.

Hoping my dissapointment will be in a reasonable range once we have eliminated the distracting issues.

 

[Randy Holmes-Farley]

Something is screwy here. I have some Apex cal fluid on order and I have ordered up a refrectometer called True Sine which supposed is designed to measure seawater not brine.

It is going to have to be pretty close between the two.

It should be if both are perfectly calibrated and functioning.

 

[Val Shebeko]

You would think that would be the case. Apex seems to have real doubts. .

Stay tuned.

 

[Randy Holmes-Farley]

You would think that would be the case. Apex seems to have real doubts. .

Stay tuned.

I think they are just expressing the idea that the values from any of these measurements have error bars associated with them and to not expect high precision from relatively inexpensive hobby devices.

 

[Val Shebeko]

I think they are just expressing the idea that the values from any of these measurements have error bars associated with them and to not expect high precision from relatively inexpensive hobby devices.

Anything outside say 10 %. +/- will cause me concern. Going to get some seawater tomorrow and dip that salinity probe. See how close it comes to 1.0350.

 

[Randy Holmes-Farley]

Anything outside say 10 %. +/- will cause me concern. Going to get some seawater tomorrow and dip that salinity probe. See how close it comes to 1.0350.

Ocean water? No reason to assume it is any particular salinity.