ATI ICP salinity vs refractometer

[Necrodaemus]

My latest ICP came back and it shows salinity lower (32.37psu) than what I'm seeing with both of my refractometers (both calibrated with BRS refracto juice, Fritz 35ppt solution, and Randy's DIY standard (73.1gr NaCl, 2000gr RODI)). My ATS refractometers both show my systems water at 35ppt after calibrating and allowing temp to equalize.
I entered all of the major elements into a calculator and saw the same salinity level as per the ATI results.
My question is, do all of those elements affect the refractive index to the point that a refractometer should be identical to the results of adding up all majors? I ask this, because Randy's DIY standard using just NaCl and pure water do not contain any of those other elements....just sodium and chloride, yet it's still recommended to use for calibrating a refractometer.
Bottom line, I just want to be sure my refractometer is accurately measuring salinity when mixing new salt water so that my water changes can help get everything back in line. I've been using All For Reef and gave done maybe 2 water changes in the last year so it's time to change my regime and get things back on track. Here is a screenshot of all my majors:

 

[NanoSteam]

I don't know the answer to your question but like me if you want to sleep well at night knowing exactly where your salinity is invest in the Tropic Marin Glass Hydrometer so there's no more guesswork.

 

[Necrodaemus]

I don't know the answer to your question but like me if you want to sleep well at night knowing exactly where your salinity is invest in the Tropic Marin Glass Hydrometer so there's no more guesswork.

I'm about to order one. I'm just concerned about durability when measuring to mix new salt water.

 

[NanoSteam]

I'm about to order one. I'm just concerned about durability when measuring to mix new salt water.

Handle with care of course but don't be scared of it either. I cut all the flow in my display and place it in there from time to time but I've also used it as a reference point to calibrate my refractometer and Hannah checker so I don't always have to pull it out.

 

[Necrodaemus]

@Randy Holmes-Farley what are your thoughts?

 

[rtparty]

After 60+ ICP tests with ATI, I can say with complete confidence to NOT trust their salinity reading. It maybe matched mine 3-4 times in those 60 tests and I always checked my water with a calibrated refractometer and a Milwaukee digital

 

[Randy Holmes-Farley Verified Community Expert]

I don't know the answer to your question but like me if you want to sleep well at night knowing exactly where your salinity is invest in the Tropic Marin Glass Hydrometer so there's no more guesswork.

How do you know it’s accurate?

 

[Randy Holmes-Farley Verified Community Expert]

@Randy Holmes-Farley what are your thoughts?

I don’t know what method they use or how accurate they are in using it, so I cannot say.

Assuming my fluid is made with the right specifications, devices that read it correctly should be accurate within their expected range of accuracy.

 

[NanoSteam]

I don't know the answer to your question but like me if you want to sleep well at night knowing exactly where your salinity is invest in the Tropic Marin Glass Hydrometer so there's no more guesswork.

How do you know it’s accurate?

Isn't the Glass hydrometer widely known to be the most accurate option?

Just to add it matches my refractometer calibrated with Two little fishes calibration fluid and home made using your recipe.

 

[BryanM]

I would trust a properly calibrated refractometer.

But I also am ordering the TM hydrometer.

 

[Randy Holmes-Farley Verified Community Expert]

Isn't the Glass hydrometer widely known to be the most accurate option?

Just to add it matches my refractometer calibrated with Two little fishes calibration fluid and home made using your recipe.

It is commonly claimed to be accurate, but folks rarely test them. What if it is not made perfectly? What it does do is typically not ever get misadjusted, so it always uses the same basic “calibration”. I’m sure they are nearly always perfectly adequate for our purposes, but to claim they are the most accurate is not, IMO, accurate.

I do not believe it is as accurate as the conductivity meter I use, which is the type of device chemical oceanographers use. The entire modern salinity scale is based on a conductivity measurement of a specific standard solution being 35 PSU (= ppt).

 

[NanoSteam]

It is commonly claimed to be accurate, but folks rarely test them. What if it is not made perfectly? What it does do is typically not ever get misadjusted, so it always uses the same basic “calibration”. I’m sure they are nearly always perfectly adequate for our purposes, but to claim they are the most accurate is not, IMO, accurate.

I do not believe it is as accurate as the conductivity meter I use, which is the type of device chemical oceanographers use. The entire modern salinity scale is based on a conductivity measurement of a specific standard solution being 35 PSU (= ppt).

I understand your reasoning for questioning the accuracy. It's always verify verify and triple verify. I now have 3 methods of testing salinity because I have obsessive issues and here's how its going:

Refractometer calibration fluid with your (Randy's) DIY solution and Two Little Fishes calibration fluid (known to be the best commercially available) match and verify calibration BUT I suppose since it's a cheap refractometer from Amazon it loses it's calibration within 24 hours.

Hannah Salinity checker was off by 3PPT from the refractometer, tried calibrating it twice with the including 35ppt solution but no dice.

TM Glass Hydrometer showed 1.026 nearly matching the refractometer.