Four Salinity Testers, Four DIFFERENT results - Which do you trust?

[Ziggy17]

Get a Tropic Marin high-precision hydrometer. Good timing: Black Friday sale at BRS:
https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html

That.

 

[FrugalReeferJon]

Tropic Marin Hydrometer for the win

 

[Euphylliaphyle]

Ignorance is bliss! But I look at it this way: I get very consistent results, very close to what I need. And isn't stability the better part of the whole point? Besides, I checked it for deviation against my reference standard, my trusty IO plastic swing arm hydrometer! lol

I say this half in jest. Do what Randy says. This will provide a point estimate of accuracy, which is a useful number. When I say, "No" to the question of "Does this require calibration?" I am thinking of calibration in terms of checking an instrument for not only accuracy, but also for repeatability, reproducibility, linearity, then adjusting the instrument accordingly. Since hydrometers cannot be adjusted, they cannot be calibrated, per se.

 

[nickng]

Hydrometer, never need to be calibrated. Especially it came with a NIST tested certificate. The tropic Marin one is good enough. 1 to 2degree variation in temperature won’t amount to any significant change in salinity readings.

 

[Biff0rz]

Get a Tropic Marin high-precision hydrometer. Good timing: Black Friday sale at BRS:
https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html

Having used everything under the sun, this is all I trust. Everything else is junk!

 

[Randy Holmes-Farley Verified Community Expert]

Having used everything under the sun, this is all I trust. Everything else is junk!

Lol

Perhaps you have just been buying cheap “junk”. The modern salinity scale is actually defined in terms of conductivity, not density or specific gravity. Why? Because high quality conductivity meters are highly accurate and more user friendly than hydrometers.

 

[RobertK]

Thank you, so many people have recommended this, that I did order it from BRS, now just have to wait a week for it to arrive (hope it's not broken in shipping),.

I recommend making an appropriate standard yourself, and not rely on others to do things properly.

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/
from it for a refractometer:

In order to provide a standard for refractometers, a solution whose refractive index is similar to normal seawater is required. Seawater with S= 35 has a refractive index of 1.3394.1 Likewise, the refractive index of different sodium chloride solutions can be found in the scientific literature. My CRC Handbook of Chemistry and Physics (57th Edition, Page D-252)4 has such a table. That table has entries for 3.6 and 3.7 weight percent solutions of sodium chloride that span the value for normal seawater. Interpolating between these data points suggests that a solution of 3.65 weight percent sodium chloride has the same refractive index as S=35 seawater, and can be used as an appropriate standard (Table 2).

This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water.

I live near the ocean. Can I use seawater that I collect at the beach to calibrate my hydrometer?

 

[nickng]

Or pay a premium for a lab grade hydrometer. https://www.fishersci.com/shop/prod...ific-gravity-hydrometers-35/11522DC#?keyword=

Or a cheap one (calibration unknown) with a build in thermometer.
https://www.homesciencetools.com/pr...LLK4odxSltcCDpGKzBwDD1FSW698hRtaoCkcqjUIosMLA

 

[EnterName]

There are various things going on here which may contribute to the issue, so bare with me for a second:

Please take a close look at 1.022 on the Instant Ocean Hydrometer. It is slightly below 30ppt as you can see on the scale. Now take a look at 1.022 on the Hygger hydrometer. It is very close to 32.8ppt and far above 30ppt.
This means your hydrometers are measuring density relative to different standards. To make readings comparable between devices, we need to use an "absolute" scale like ppt.

Let's try using the ppt scales for comparison instead:

• Instant Ocean: 1.023 ≈ 31ppt
• Hygger: 1.024 ≈ 35.5ppt
• Coralife: 1.028 ≈ 37.8ppt
• Refractometer (assuming d20/20 = d68/68 standard, which is most common): 1.027 ≈ 35.5ppt

Unfortunately the readings are still all over the place, so what is going on?
There are various factors contributing to standard reading errors, such as temperature compensation and salt composition, but looking at these readings, I assume something else is going on.
During my research, I have found these instructions on how to prepare the Hygger before using it,

and I assume the other hydrometers could use a similar treatment, as well. As far as I know, swing arm hydrometers like to trap bubbles which cause reading errors and they are generally known for their erroneous readings. I rarely suggest buying another product because as long as a device gives repeatable measurements and you know its quirks, you can make it work. However, in this case it might make sense to use a high quality glass hydrometer instead. It doesn't matter too much if the hydrometer is off by 0.001 or 0.002 as long as the results are repeatable over time. Your fish and corals won't mind 1 or 2 ppt difference.

 

[Biff0rz]

Lol

Perhaps you have just been buying cheap “junk”. The modern salinity scale is actually defined in terms of conductivity, not density or specific gravity. Why? Because high quality conductivity meters are highly accurate and more user friendly than hydrometers.

True, but, how much do those cost? Because the ones available(and marketed) to the typical hobbyist (Neptune Apex Sg Meter & Hanna Sg Tester) are JUNK. The TM Hydrometer is the best of both worlds for a hobbyist - closest in accuracy without breaking the bank.

For example: Fisher = $520. Now, if the TM is off by 1-2% from that, good enough.

 

[reefernc02]

I personally love my Milwaukee salinity meter it’s never steered me wrong always matches icp values

 

[Randy Holmes-Farley Verified Community Expert]

I live near the ocean. Can I use seawater that I collect at the beach to calibrate my hydrometer?

No, unless you somehow know its salinity.

 

[Randy Holmes-Farley Verified Community Expert]

True, but, how much do those cost? Because the ones available(and marketed) to the typical hobbyist (Neptune Apex Sg Meter & Hanna Sg Tester) are JUNK. The TM Hydrometer is the best of both worlds for a hobbyist - closest in accuracy without breaking the bank.

For example: Fisher = $520. Now, if the TM is off by 1-2% from that, good enough.

I bought a good one on eBay, as have many others. :)

 

[reefernc02]

True, but, how much do those cost? Because the ones available(and marketed) to the typical hobbyist (Neptune Apex Sg Meter & Hanna Sg Tester) are JUNK. The TM Hydrometer is the best of both worlds for a hobbyist - closest in accuracy without breaking the bank.

For example: Fisher = $520. Now, if the TM is off by 1-2% from that, good enough.

I bought a good one on eBay, as have many others. :)

Are you talking about the fisher I’m a huge gear nerd and thought about buying one just for giggles

 

[Randy Holmes-Farley Verified Community Expert]

Are you talking about the fisher I’m a huge gear nerd and thought about buying one just for giggles

For decades I used an Orion model 128 with a 4 electrode probe. It finally bit the dust and I bought an old VWR brand probe and meter on eBay.

 

[mcarroll]

Thread after thread like this lately...

Seriously, did everyone's warranty run out at the same time??!! What gives?

Perhaps worth pointing out that repeatability is more important than accuracy in your measurement tool of choice. (Tho having both is nice!)

Both fish and corals are pretty adaptable and do not require a precise salinity....but both appreciate a salinity that is stable over the longer term.

@Steverd, IMO there might not be anything wrong with any of the devices you started with. Just pick your favorite one and stick with it so your results are consistent.

 

[mcarroll]

For decades I used an Orion model 128 with a 4 electrode probe. It finally bit the dust and I bought an old VWR brand probe and meter on eBay.

What is upkeep like for a piece of gear like that. Is it zero maintenance? Do you have to calibrate it daily? (Hourly!? Minute by minute!?!)

Kidding in the spirit of the zeitgeist. ;)

But seriously....the books all mention conductivity as better, but don't go much in to the practical side of owning/operating one except to say they require calibration.

 

[Narideth]

Having had salinity issues in the past, I got the TM hydrometer to double check my salinity periodically.

Back when I was only like 6 months in, I took test water to 3 different LFS and got answers all over the place because I had questions due to a suspiciously low magnesium test of all things, that ended up with an overall salinity in my tanks of 1.017. The refractometer calibration I'd been using was that far off. I have more personal peace of mind having the simple, fancier but also relatively affordable tool in my kit I can rely on if I have concerns.

 

[Euphylliaphyle]

Thread after thread like this lately...

Seriously, did everyone's warranty run out at the same time??!! What gives?

Perhaps worth pointing out that repeatability is more important than accuracy in your measurement tool of choice. (Tho having both is nice!)

Both fish and corals are pretty adaptable and do not require a precise salinity....but both appreciate a salinity that is stable over the longer term.

@Steverd, IMO there might not be anything wrong with any of the devices you started with. Just pick your favorite one and stick with it so your results are consistent.

I would add to that:
Perform 3-4 successive tests on the same sample each time you test, at least for a while, then do that occasionally ongoing to keep things honest. This will help identify test-to-test inconsistencies in the operator-device system. Learn from such inconsistencies, e.g., Did bubbles on the device cause it? - then remidiate the procedure accordingly. This is not exactly a full measurement system analysis, but imo will get to the heart of what we need as aquarists from our salinity measurements.
I was able to get pretty consistent results from my IO swing arm, but it was a bit finicky (swing arm bubble entrapment) and I much prefer the TM glass precision hydrometer.

 

[mcarroll]

I would add to that:
Perform 3-4 successive tests on the same sample each time you test, at least for a while, then do that occasionally ongoing to keep things honest. This will help identify test-to-test inconsistencies in the operator-device system. Learn from such inconsistencies, e.g., Did bubbles on the device cause it? - then remidiate the procedure accordingly. This is not exactly a full measurement system analysis, but imo will get to the heart of what we need as aquarists from our salinity measurements.
I was able to get pretty consistent results from my IO swing arm, but it was a bit finicky (swing arm bubble entrapment) and I much prefer the TM glass precision hydrometer.

I wonder if I'd kept my swing arm rinsed clean (vs allowing sw residue to buildup) if the issues with it would have been less? (I may dig mine out and mess around with it someday soon.)