Salinity differences between ICP and Home

[Randy Holmes-Farley Verified Community Expert]

I have had the same issues. Both ICP tests I sent is this year (ATI) came back low on salinity. I calibrate my refractometer about 4-6 times a year. I can’t explain why they get a lower reading than I do. Maybe they use other parameters to determine salinity?

How far off?

 

[REEFRIED!]

How far off?

I’ve been consistently at 35ppt (1.026 sg). The two tests showed 32.62 and 32.82. ATI uses PSU which I believe is the same as ppt?

 

[Uncle99]

Same for me, salinity off.
I wonder if processing time affects this measure?
My tests are done within minutes of taking a water sample.
My ICP took 6 weeks.

 

[rtparty]

After 60+ ICP tests with ATI, I found no value in their salinity measurements. It never once matched mine and I used 3 calibrated tools to be as close to 35ppt as possible. I even include a “4th tool” since I weighed all my water and salt each time just to remove another variable.

It never matched. It was close at times but I could almost guarantee it was 10% low each time

 

[Randy Holmes-Farley Verified Community Expert]

I’ve been consistently at 35ppt (1.026 sg). The two tests showed 32.62 and 32.82. ATI uses PSU which I believe is the same as ppt?

I would just point out that the company that I know of that sells refractometers to hobbyists (Milwaukee MA887) that gives an accuracy claim only claims +/- 2 ppt accuracy.

Couple that with uncertainties how and with what accuracy any icp company provides salinity data, and it is not altogether surprising there will be discrepancies.

 

[BeanAnimal]

I will say that when I use my Milwaukee refractometer set to PSU, I get equal results to the Oceamo.

I will say that i think that tool is rubbish. I had two both are in a landfill now.

 

[Miami Reef]

I sent a new ICP after making some changes to my ionic balance, and the results are much closer. I don’t know if that had anything to do with it.

The TM hydrometer measured 1.0263 the day I sent the results.

 

[Randy Holmes-Farley Verified Community Expert]

I sent a new ICP after making some changes to my ionic balance, and the results are much closer. I don’t know if that had anything to do with it.

The TM hydrometer measured 1.0263 the day I sent the results.

I don’t know either, but thanks for the update!

 

[BeanAnimal]

I am inclined to trust the TM hydrometer if it matches a standard that also matches other instruments.

I can see (somewhat) why a density and conductivity test (both in theory calibrated) may not match when the conductivity probe may not be able to account for some ions in context to density. I spent considerable time trying to wrap my head around the ever evolving equation of state for seawater. Even if it is the "standard" I don't see how it really can be defined like other "standards" (a millimeter, a gram, time, etc.).

 

[KStatefan]

My results from Oceamo are about the same as what I get with a hydrometer adjusted for the temperature. Last 5 test sent in.

TM Hydrometer	Oceamo ICP	Delta
35.0	34.9	0.1
34.5	34.5	0.0
34.2	34.1	0.1
35.3	35.2	0.1
34.5	34.5	0.0

 

[REEFRIED!]

I would just point out that the company that I know of that sells refractometers to hobbyists (Milwaukee MA887) that gives an accuracy claim only claims +/- 2 ppt accuracy.

Couple that with uncertainties how and with what accuracy any icp company provides salinity data, and it is not altogether surprising there will be discrepancies.

Do you recommend a decent backup way of measuring my salinity? Keep in mind I’d rather not break out the rubber gloves, beakers, and centrifuges!!!

 

[BeanAnimal]

Buy the TM precision floating hydrometer.

 

[Randy Holmes-Farley Verified Community Expert]

Do you recommend a decent backup way of measuring my salinity? Keep in mind I’d rather not break out the rubber gloves, beakers, and centrifuges!!!

What do you use now and how do you calibrate it?

 

[irischan]

Different methodology will give different test result. Even the same metholdogy, ie ICP, different companies have different protocols, different analyser brands, etc to perform the ICP tests. As long as you stick to one test method and your tank is doing good, then I think you are good. If you really want to scratch the itchy, one approach you can do is using the average of the test results as your final result, to minimize the bias from different methodolgies and let the final result hopefully closer to the true value.

Note from a ICP lab guy.

 

[REEFRIED!]

What do you use now and how do you calibrate it?

I use a refractometer and I use the BRS calibration fluid.

 

[REEFRIED!]

I was thinking of buying the TM hydrometer that people have spoken about in this thread. Thoughts?

 

[Randy Holmes-Farley Verified Community Expert]

F was thinking of buying the TM hydrometer that people have spoken about in this thread. Thoughts?

It’s a fine tool. A little laborious to use in some settings (equilibrating fish in a shipping bag, for example) but would be good to double check other devices. I would check its accuracy at least once.

 

[REEFRIED!]

It’s a fine tool. A little laborious to use in some settings (equilibrating fish in a shipping bag, for example) but would be good to double check other devices. I would check its accuracy at least once.

I just ordered a TM Hydrometer. How would I go about checking its accuracy? Especially if I am questioning the results of my refractometer.

 

[eliaslikesfish]

am I the only one that just got a good quality refractometer, calibrate it as needed, and trusts? never steered me wrong.

 

[REEFRIED!]

am I the only one that just got a good quality refractometer, calibrate it as needed, and trusts? never steered me wrong.

That was me, until two ICP tests both showed a lower salinity number.