Salinity Checking … What To Trust …

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DWill

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What to trust…

I bought a Hanna salinity checker in March. The Hanna works well, it tracks my old school refractometer nearly perfectly; as long it’s it’s calibrated.

After the first few weeks of use it hold calibration well, usually a month or so. My experience is that in the first 2-3 weeks it has to be calibrated often, after a while it’s good to go. The other “issue” I’ve had is that the checker just doesn’t last long, I don’t know if it the carbon fiber probes, bad luck, or what the problem may be. I’ve replaced the checker under warranty twice in 6 months. The last time I had it replaced was a couple weeks ago.

During the weeks long sales last week I ordered a Milwaukee digital refractometer. It came in today.

I calibrated it and checked the water in my display. 1.031 was the reading.
That surprised me so I recalibrated, this time waitin a full minute to let the Distilled water temp equalize, I did the did the same the calibration check fluid. Checked the tank, again waitin a full minute … 1.029

I checked against my Apex salinity probe, which I never use for anything other than maybe a general trend monitor. The Apex reads 34.6 so “about” 1.026 (I keep my system at 1.026)

I break out the Hanna… 1.025.

I calibrate and use my refractometer … 1.026

I recalibrate and check with the Milwaukee … 1.030

I used the exact same procedure for everything; waithing one full minute before checking the result.

So…

Apex 34.5 (generally unreliable)
Hanna checker 1.025
Refractometer 1.026
Milwaukee 1.030 (1.029 was closest but still out of spec assuming any of the others is accurate)

I’m kinda disappointed actually. The Hanna seem accurate but it life span seems to short and I don’t know how many times Hanna will warranty their product before they just tell me no. Even though they know the issue exists because before I finished describing the problem the tech support guy was telling me how to attempt to “fix” it. It’s obviously a know issue.

The Milwaukee seems to be out of range. I seriously thinking about returning it now.

The old refractometer gives me what looks to be accurate results as long as I calibrate before each use.

So, what would you do?

What’s your experience with the Milwaukee?
 

HuduVudu

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I have a Milwakee. It is reliable and I trust it, but I don't have anything to compare it too. The more I read the less interested I am in refractometers. I remember when they were a $100. I don't know if there is a difference between then and now, but I have totally gone away from them.

I know that the LFS I go to always has their refractometers out of cal and their specfic gravity is all over the place.

I am mulling getting a hydrometer as a sanity check. FWIW.
 

Randy Holmes-Farley

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rkpetersen

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Getting salinity measurements to agree is trickier than it should be.
The Milwaukee isn't necessarily the most accurate. Also note that Hanna makes an electronic refractometer which is exactly the same device as the Milwaukee, just a different color case.
You can make up your own standard, as mentioned. 35 g table salt in 1000 ml water is (approximately) 35 ppt.
You might try different calibration solutions. Some are designed only to be used with electronic conductivity meters and won't necessarily give an accurate number with a refractometer.
Another option is to get a precision hydrometer, like this one. This thing is huge, 13" in length, and graduated at 0.0001 SG increments. Seems quite accurate. Also can't go out of calibration. Too big to use in many sumps though.
 
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DWill

DWill

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I have a Milwakee. It is reliable and I trust it, but I don't have anything to compare it too. The more I read the less interested I am in refractometers. I remember when they were a $100. I don't know if there is a difference between then and now, but I have totally gone away from them.

I know that the LFS I go to always has their refractometers out of cal and their specfic gravity is all over the place.

I am mulling getting a hydrometer as a sanity check. FWIW.
I’m thinking the same thing actually.
 

Philly Reefer

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I was going to buy the milwaukee instead of hanna last week. In the end I didn't, I thought might as well get the high precision hydrometer. That is the most accurate one.
So.. I'll be buying that next..
 
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DWill

DWill

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Getting salinity measurements to agree is trickier than it should be.
The Milwaukee isn't necessarily the most accurate. Also note that Hanna makes an electronic refractometer which is exactly the same device as the Milwaukee, just a different color case.
You can make up your own standard, as mentioned. 35 g table salt in 1000 ml water is (approximately) 35 ppt.
You might try different calibration solutions. Some are designed only to be used with electronic conductivity meters and won't necessarily give an accurate number with a refractometer.
Another option is to get a precision hydrometer, like this one. This thing is huge, 13" in length, and graduated at 0.0001 SG increments. Seems quite accurate. Also can't go out of calibration. Too big to use in many sumps though.
I just ordered it.
 
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DWill

DWill

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I use a hanna checker and seems like its been on the money . I have a refractometer and hydrometer but they seem to have issues after a while
ya... my Hanna is awesome... until it stops working... seems like every four months or so it needs to be replaced.
 

HB AL

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Not sure what brand refractometer i have but I really never have to calibrate it. I have a 30 year old swing arm that on occasion I use to compare the 2 of them and they are both always spot on.
 

Randy Holmes-Farley

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Not sure what brand refractometer i have but I really never have to calibrate it. I have a 30 year old swing arm that on occasion I use to compare the 2 of them and they are both always spot on.

Brings to mind a story I read in a science book years ago.

Many years ago, when trying to nail down exactly when an earthquake took place so that the time for the earth movement to reach certain distances could be determined, the scientist was out west in a town with a military fort.

He asked everyone what time the earthquake hit, and got the same number from many people.

But then he thought, how do these people know what time it actually is?

Some referred to the clocks in a jeweler's shop, and some to a cannon fired off at the fort every afternoon at 5 ppm.

When he asked at the jeweler's shop how he set his clocks, the was told that they set it exactly to the firing of the cannon at 5 pm.

When he asked at the fort how they determine when to fire the cannon, the soldier in charge said he sets his watch to match those in the jewler's shop... lol
 

Dr. Jim

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I would make solutions to check each of those with a 35 ppt solution, and see which are accurate. Especially if you have a kitchen or lab scale.

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
Randy, I have made a standard according to your recommendation (3.65 g NaCl in 96.35 ml water) and appreciate you making this available to us. But I am wondering how significant "measurement error" comes into play so I just wanted to work a hypothetical scenario involving error.

Measuring water volume should be relatively accurate, but more error might be expected with dry wt measurement. A scale may have a + or - margin of error of 0.1 g, so the 3.65 g NaCl may actually be 3.55 to 3.75. Let's say it is actually 3.75 g (2.7% error) and the water measurement is actually 96.00 (0.36% error).

I'm not sure if this is proper math, but I think you can add the two errors and get a total error of 3.06%. So if the refractometer reading is 1.026 I think we multiply 0.026 by 3.06% to get an actual S.G. of 1.0268 (0.026 + 0.0007956). If this is correct, then, to be practical, one might assume the S.G. error of the DIY to be as much as about 0.001 (i.e. 1.025 to 1.027 when we calibrate at 1.026.)

So it seems that one needs a very accurate scale to get a more precise value (and using tablespoons would most likely lead to an even greater). I'm sure all the companies making calibration solutions have the same potential errors, so I'm not saying anything negative about your DIY.....just trying to get a grasp on how much I can trust my own measurements. (Again, thank you for providing your DIY for us to use!)
 

Dr. Jim

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I have a Milwaukee refractometer which generally runs 0.001 higher than what calibration standards show. But I can never get different standards to agree, including 3 brands plus Randy's DIY, using a standard refractometer and the Milwaukee.

I recently ran an ICP test with OCEAMO. Dr. Denk assured me that their calibrated conductivity meter is very accurate. If so, then that means the Tropic Marin High Precision hydrometer matches up best with that reading and is the instrument that I am trusting the most now.
 

Randy Holmes-Farley

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Randy, I have made a standard according to your recommendation (3.65 g NaCl in 96.35 ml water) and appreciate you making this available to us. But I am wondering how significant "measurement error" comes into play so I just wanted to work a hypothetical scenario involving error.

Measuring water volume should be relatively accurate, but more error might be expected with dry wt measurement. A scale may have a + or - margin of error of 0.1 g, so the 3.65 g NaCl may actually be 3.55 to 3.75. Let's say it is actually 3.75 g (2.7% error) and the water measurement is actually 96.00 (0.36% error).

I'm not sure if this is proper math, but I think you can add the two errors and get a total error of 3.06%. So if the refractometer reading is 1.026 I think we multiply 0.026 by 3.06% to get an actual S.G. of 1.0268 (0.026 + 0.0007956). If this is correct, then, to be practical, one might assume the S.G. error of the DIY to be as much as about 0.001 (i.e. 1.025 to 1.027 when we calibrate at 1.026.)

So it seems that one needs a very accurate scale to get a more precise value (and using tablespoons would most likely lead to an even greater). I'm sure all the companies making calibration solutions have the same potential errors, so I'm not saying anything negative about your DIY.....just trying to get a grasp on how much I can trust my own measurements. (Again, thank you for providing your DIY for us to use!)

The recipe can be done on any volume that makes best use of your measuring devices. 3.65 g/100 g, or 36.5 g/L, etc.

Since few folks using refractometers report (or care much) about high precision, let's say one in interested in a sg of 1.0259 to 1.0269 (35 ppt +/- 0.66 ppt). Folks can scale their desired precision up or down as as needed.


That range would need 3.58 to 3.72 g per 100 g total weight. Or better still, 35.8 to 37.2 grams in 1 kg total weight. Both the salt and the water can be measured at that accuracy using a 0.01 gram precision scale.

Amazon sells one for $14.


If you are worried about the accuracy, one can get a set of calibration weights for $12:


The volume measurement of the salt using Mortons will also be accurate enough, I believe, if done as I suggest.
 

PghReef

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I got frustrated and tired of calibrating my refractometer. I'd get 3 different results using 3 separate bottles of calibration solution on the same refractometer.

Now I just taste the water and can tell you if its within range

All seriousness I ordered a glass hydrometer. Just turn off my return pump and bob it in place in the corner overflow. Take note of the measurement and Restart my return pump. Super accurate and no moving parts or things to calibrate so if it's off it's off the same every reading from now until forever.

FWIW I tested it against my recently calibrated refractometer and it read the same, only no more blue line to try and decipher exactly where it is and the glass hydrometer gives you more precision with an extra decimal so my tanks at 1.0265
 

Saltyreef

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Brings to mind a story I read in a science book years ago.

Many years ago, when trying to nail down exactly when an earthquake took place so that the time for the earth movement to reach certain distances could be determined, the scientist was out west in a town with a military fort.

He asked everyone what time the earthquake hit, and got the same number from many people.

But then he thought, how do these people know what time it actually is?

Some referred to the clocks in a jeweler's shop, and some to a cannon fired off at the fort every afternoon at 5 ppm.

When he asked at the jeweler's shop how he set his clocks, the was told that they set it exactly to the firing of the cannon at 5 pm.

When he asked at the fort how they determine when to fire the cannon, the soldier in charge said he sets his watch to match those in the jewler's shop... lol
Wasnt that the same day they invented NIST? Lol
 

birdy123

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I use the Hanna tester and found it to be very accurate, although I did have a replacement as the temperature probe side of it was not reading correctly and therefore giving the wrong salinity.
I found if you closely watched the temperature reading you could see the digital display faultier and then get a false reading.
Maybe a batch of Hanna checkers faulty.??
 
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