Salinity checking journey - finally landed on TM Hydrometer

[Gatortailale]

After over 22 years in salt hobby, I found a new happy place in checking my salinity, and my old eyes appreciate it.  I picked up a Tropic Marin High Precision Hydrometer and going old school has will be my last stop on gadgets.  They can be had for $37 and up depending on the vendor.  The TM hydrometer is hand crafted to read water at at 77° F (25° C) - which is great for most of us running tanks around 77-78 F.  The thing I like most is it never needs to be re-calibrated.  

 

 

Despite recently trying to calibrate my refractometer the TM hydrometer showed I was off.  Likewise, I was able to recalibrate my apex probe with fresh calibration fluid and have confidence now that probe reading is closer in line to what hydrometer is reading tank water at.  

 

BRS has a handy video to give overview of the TM hydrometer.

 

Found this handy article on Temp correction for hydrometers:  https://reefkeeping.com/issues/2004-07/rhf/index.php

 

Simple Salinity Correction Calculator website for unit calibration of 77 F   https://www.hamzasreef.com/Contents/Calculators/SalinityCorrection.php

 

Here is discussion on Temp conversion chart for TM Hydrometer.

 

Conversion chart from R2R discussion:

Temp Chart Hydro.pdf

 

Note: I picked up a plastic graduated cylinder kit that had sizes up to 250 ml as well as plastic beakers of various sizes - while the Hydrometer will work in the 250 ml cylinder, I'm going to get a 500 ml plastic one as I think that will work better.

 

PS: I bought 2 because it may be a bit delicate and the price was reasonable to have backup on hand.

 

As for verifying my water temps, I picked up one of these Cole-Parmer Traceable Lollipop™ Waterproof Thermometer Ultra with Calibration; ±0.4°C accuracy at tested points and can now calibrate Apex probes, InkBird heater controllers and water temp for Hydrometer.

 

https://www.coleparmer.com/i/traceable-lollipop-waterproof-thermometer-ultra-with-calibration-0-4-c-accuracy-at-tested-points/9876849?searchterm=EW-98768-49

 

 

 

[gws3]

I reached the same conclusion as you Craig, I'm using a TM hydrometer as my most trusted source for salinity measurements. It was the clear winner after years of struggling with optical refractometers and never really trusting the conductivity based ones.

 

I use about 400 ml in a 500 ml plastic graduated cylinder. Drop it in, spin, and check it in a minute or two when it settles. When I check salinity I also use a Hanna HI98319 tester (conductivity) as well. The Hanna typically reads about 0.8-1.1 ppt lower. I'm not sure why it reads so much lower, it does this regardless of calibration.

 

When I got the TM hydrometers I even went as far as to make a standard with Morton's Iodized Salt per some articles Randy Holmes Farley wrote. At 77F the solution should be 1.0266. One TM hydrometer reads spot on at 1.0266, the other reads at 1.0264. So, very happy with the accuracy of them. The Hanna probe reads about 1.0-1.1 ppt low in this standard I created.

[gws3]

Oh, and for temp probe calibration I use another old school device... a mercury filled glass thermometer. Forget the brand, but it meets ASTM 17F. Never requires calibration and it'll never change. Just have to handle it carefully. Also, they're difficult to acquire as they can't be shipped to Maryland due to the Mercury. Not sure if the same rules apply in Virginia.

[DaJMasta]

It seems like a lot of people are in agreement that a properly calibrated hydrometer is the best choice, but it's so much more effort and saltwater required to test each time.

 

For my use case (checking salinity maybe a dozen times a week for small saltwater batches, sometimes as small as a gallon), I've been pretty happy with my Milwaukee MA887, but it's by no means perfect.  I will do a minimum of three tests, with some extra volume in the well for the first test to help find thermal equilibrium with the sample and get any residual salt out of the well.  I haven't had issues with long term drift or stray light, but it's not uncommon to see salinity change over subsequent readings as it comes up or down to temperature and I see the occasional reading increase with every measurement (to absurd levels with more checks), only to empty the well, put in another sample of the same stuff, and get a proper reading - not sure about that one.

 

What I'd really love, though, is something that would give me more than 1ppt worth of resolution.  A tenth of a ppt would make it much, much easier to see long term salinity trends in the tank - which I know mine has because of live phyto/copepod dosing, and the 1ppt resolution of the MA887 (and virtually everything else) seems too coarse.

I've also had some issues with handheld optical refractometers, and I think it's actually been physical bump related, though even with a gentle tough, I ran into drift issues even in the course of a week or two.  The electronic one needs just a few drops, a few less steps, and seems to be both consistent and stable provided you are doing several tests on the same sample and retesting if you suspect outliers.

 

I got my hands on a Reichert-Jung ABBE Mark II, but while it powers up, it doesn't seem to respond to the control buttons, so I've got some poking around to see if it actually works and then whether this used one performs as one should.

[Johnny Ho]

I also do use TM hydrometer to calibrate Milwaukee MA887 like every two months or so.  So far, they both are lining up close to each other.

[lowsingle]

I too struggle with salinity, I use a refractometer and will get different readings from two different calibration fluids that are supposed to be the same ppt.  Maybe I should look more closely at the hydrometer.  Thanks for posting your strategy.

 

Darren

[gws3]

On 3/1/2024 at 3:28 PM, DaJMasta said:

It seems like a lot of people are in agreement that a properly calibrated hydrometer is the best choice, but it's so much more effort and saltwater required to test each time.

 

For my use case (checking salinity maybe a dozen times a week for small saltwater batches, sometimes as small as a gallon), I've been pretty happy with my Milwaukee MA887, but it's by no means perfect.  I will do a minimum of three tests, with some extra volume in the well for the first test to help find thermal equilibrium with the sample and get any residual salt out of the well.  I haven't had issues with long term drift or stray light, but it's not uncommon to see salinity change over subsequent readings as it comes up or down to temperature and I see the occasional reading increase with every measurement (to absurd levels with more checks), only to empty the well, put in another sample of the same stuff, and get a proper reading - not sure about that one.

 

What I'd really love, though, is something that would give me more than 1ppt worth of resolution.  A tenth of a ppt would make it much, much easier to see long term salinity trends in the tank - which I know mine has because of live phyto/copepod dosing, and the 1ppt resolution of the MA887 (and virtually everything else) seems too coarse.

I've also had some issues with handheld optical refractometers, and I think it's actually been physical bump related, though even with a gentle tough, I ran into drift issues even in the course of a week or two.  The electronic one needs just a few drops, a few less steps, and seems to be both consistent and stable provided you are doing several tests on the same sample and retesting if you suspect outliers.

 

I got my hands on a Reichert-Jung ABBE Mark II, but while it powers up, it doesn't seem to respond to the control buttons, so I've got some poking around to see if it actually works and then whether this used one performs as one should.

 

Look at the Hanna HI98319, it'll give you the tenth of a ppt you're looking for. Mine consistently reads 0.8-1.1 lower than the TM hydrometer, but it's consistent. What you could do ii check the HI98319 against the hydrometer every month or two, but use the HI98319 regularly. It can be used in tank, so it doesn't require any saltwater to be removed.

[DaJMasta]

Interesting, I may end up getting one, but the pen style also needs a larger sample (though maybe an ounce in a shotglass would do.)

I wonder what benefits there are to electrical conductivity vs. refractometry vs. specific gravity (a hydrometer.)  I feel like most of the professional/research solutions I hear about are electrical conductivity based, but that may just be because when your probe is fully immersed in water, the alternatives are just more complicated to manage than dealing with whatever problems are inherent to EC measurements.

[BowieReefer84]

On 2/27/2024 at 7:33 AM, gws3 said:

Oh, and for temp probe calibration I use another old school device... a mercury filled glass thermometer. Forget the brand, but it meets ASTM 17F. Never requires calibration and it'll never change. Just have to handle it carefully. Also, they're difficult to acquire as they can't be shipped to Maryland due to the Mercury. Not sure if the same rules apply in Virginia.

 

For Temp, I use a thermapen one. They include a NIST calibration certificate.

https://www.thermoworks.com/thermapen-one/?utm_source=google_shopping&utm_medium=organic&gad_source=1&gclid=CjwKCAjwwr6wBhBcEiwAfMEQs0pgtBK1zltsR21Gaqh_ipOTKAtmC__DZ8s6G0n_BgVw-Qh76BaEcBoCet0QAvD_BwE

 

 

[nburg]

Good post to raise awareness!

 

I am done with refractometer calibration solution. When new, they are correct at 35 ppt, but over time they must evaporate water because they always go up. I had some corals doing poorly and wasn't sure why. Someone gave me some calibration solution with a refractometer they were getting rid of (nice to have backups) and I was like hey, this is 2 ppt too low... then i got to thinking, and got a third one brand new... it was 2 ppt low as well. I was frustrated with a pretty big difference in the 3 and bought the TM hydrometer and turns out my main calibration solution was 37 ppt instead of 35 ppt. I continued to use the new, correct fluid to spot check every week but thankfully if my refractometer comes back wonky, I compare the solution to my TM hydrometer. Sure enough, the third bottle drifted. conveniently enough, I run my tank at 77F so no temp compensations needed. 

 

Now I will calibrate my refractometer to my hydrometer every couple weeks. If my DT or my fresh mixed saltwater come back weird (they're usually consistent) I will spot check.  

Edited April 7 by nburg

[nburg]

On 3/2/2024 at 8:52 AM, lowsingle said:

I too struggle with salinity, I use a refractometer and will get different readings from two different calibration fluids that are supposed to be the same ppt.  Maybe I should look more closely at the hydrometer.  Thanks for posting your strategy.

 

Darren

I've found the cal solutions will drift over time, maybe from evaporating water?

[DaJMasta]

It's possible, most plastic bottles are liquid proof but don't necessarily have a vapor barrier to block all water vapor from entering/leaving, but the amount should be very small, and should go away in measurement noise if the amount of solution is large.

 

It could be that some test solutions separate or precipitate over time, but I imagine this isn't super likely either.  Maybe the drift you're seeing is in the measurement equipment, temperature compensation, or something else.  A way to check would be to weigh the solution after using it and write it on the bottle, if the weight is different before you use it again, then something is certainly up and drift is likely.