Four instruments.. four very different salinity readings.

[gideon2086]

Milwaukee is supposed to be calibrated with distilled water. Can't use 35ppt on it.

Right, I didn't calibrate it with 35ppt.

 

[gideon2086]

Depending on the refractometer, using ro/di for calibration may be theoretically ok, but it may also be inherently inaccurate and it is worth checking every device in a 35 ppt standard.

Even hydrometers should be checked and must be adjusted for temp issues.

I personally wonder how much of the faith in the accuracy of glass hydrometers is based on the fact that few people test them in 35 ppt standards to actually know.

I will do this, thank you for the advice.

 

[Rmckoy]

Aside from the refractometer they are all close enough.

Lots of factors to consider. When were they last properly calibrated? Were all of the samples the same temperature? Was that temperature the same as the fluid used to calibrate the tool? The Hydrometer is probably your best bet provided that it is a seawater Hydrometer and not intended for another use.

Is it a floating bobber style hydrometer or a swing arm style ?

calibration solution for refractometer arw
Different from conductive meters .
I don’t think temp would matter for most except for the floating hydrometer

 

[gideon2086]

Is it a floating bobber style hydrometer or a swing arm style ?

calibration solution for refractometer arw
Different from conductive meters .
I don’t think temp would matter for most except for the floating hydrometer

It's a swing arm. I ordered the tropic marin glass hydrometer. I've got hundreds invested in salinity testers at this point, may as well keep it going.

 

[Muffin87]

Using the Dupla Marin hydrometer as a hardware salinity reference | Reef Builders | The Reef and Saltwater Aquarium Blog

The Dupla Marin high resolution Hydrometer came along at a time when we are really becoming quite critical about salinity measurement. This large, oversize hydrometer is specially designed to measure…

reefbuilders.com

I believe in cases like this it's best to have this combo around for double checking:

1. Precision glass hydrometer from either Dupla Marine or Tropic Marin
2. Hanna Instruments HI98509-1 Checktemp 1 for temperature correction

 

[Rmckoy]

It's a swing arm. I ordered the tropic marin glass hydrometer. I've got hundreds invested in salinity testers at this point, may as well keep it going.

I remember in the 90’s when I first started reefing there was a floating hydrometer available and it was cheaper than the swing arm styles. .
I hated it

funny thing years later Tm has one and it’s one of the most accurate instruments .
Even though it was a pain to use . I wonder if the other brand was as accurate ?

 

[Jay Hemdal]

Refractomer - 1.030
Hydrometer - 1.025
Hannah Digital - 1.023
Milwaukee Digital - 1.027

This is a bit ridiculous. Which of these do I trust?

I’ve run into the same issue, but with not quite that much range. I have a German glass laboratory hydrometer that I use as my standard (within proper temperature).
I’ve seen people give a bias to digital meters that may not be justified, but those numbers look so darn accurate (grin).
Here is an article I wrote on this subject:

Measuring Salinity / Specific Gravity in Aquariums

This article gives an overview of measuring specific gravity / salinity in aquariums.

www.reef2reef.com

Jay

 

[Kadosira]

Our Hanna reads .003 low. Properly calibrated and all, just doesn't read correctly. We calibrated it twice with the solution and had our LFS test and calibrate it as well. The owner said he's seen that happen a couple times with the Hanna readers.

 

[gideon2086]

Our Hanna reads .003 low. Properly calibrated and all, just doesn't read correctly. We calibrated it twice with the solution and had our LFS test and calibrate it as well. The owner said he's seen that happen a couple times with the Hanna readers.

Call them, their customer service is great. They'll likely replace it regardless of the age.

 

[Jeeperz]

Depending on the refractometer, using ro/di for calibration may be theoretically ok, but it may also be inherently inaccurate and it is worth checking every device in a 35 ppt standard.

Even hydrometers should be checked and must be adjusted for temp issues.

I personally wonder how much of the faith in the accuracy of glass hydrometers is based on the fact that few people test them in 35 ppt standards to actually know.

But on the last paragraph, at least at proper temp it will always read the same, no calibration to be out of whack. Unless it was made wrong

 

[Spare time]

I would test each against RODI which should be 1.000 (or close to..)

That might not yield the best results for the refractometer as I think they are less accurate the further away from the calibration point. I'm not sure why but there are threads on here talking about it in regards to why rodi can't be used as a calibration fluid and be as accurate

 

[Randy Holmes-Farley]

Milwaukee is supposed to be calibrated with distilled water. Can't use 35ppt on it.

You must use ro/di (or any pure fresh water) for calibration of it, but you can (and imo, should) still check it using a standard.

It also has a +/- 2 ppt (+/- 0.002 sg) uncertainty range based on the manufacturer claim, which makes it consistent with all of the devices reported by the OP. That means the true value could be anywhere between sg = 1.025 and 1.029.

 

[Randy Holmes-Farley]

But on the last paragraph, at least at proper temp it will always read the same, no calibration to be out of whack. Unless it was made wrong

Exactly. Why believe they were all properly made if you never, ever check it?

 

[Randy Holmes-Farley]

Our Hanna reads .003 low. Properly calibrated and all, just doesn't read correctly. We calibrated it twice with the solution and had our LFS test and calibrate it as well. The owner said he's seen that happen a couple times with the Hanna readers.

I am not doubting that it happened, but that may be a problem with the calibration fluid or temperature corrections.

 

[MBruun]

Using a hydrometer, especially a lab-grade, you will have to adjust for the temperature, but they the result are then very exact since a hydrometer cannot be calibrated.
I recommend https://reefapp.net/da/salinity-calculator and use the unit g/cm3 - Density

 

[Kadosira]

I am not doubting that it happened, but that may be a problem with the calibration fluid or temperature corrections.

We used a new pack of solution every time we calibrated at home, all at the same room temperature of roughly 72°F. When we took it to the LFS, we bought a pack of solution from them which is kept at room temp of roughly 74° and had them calibrate it then test it. Beyond that, I'm not sure how else we could calibrate it or change something.

 

[Snoopy 67]

Temperatures @ which instruments have been calibrated should be listed in the literature.
This is where you should be. My refractometer says 77 degrees Farenheight.
Temperature differences will affect results.