Tropic Marin High Precision Hydrometer range and accuracy

[BradB]

I just bought a Tropic Marin High Precision Hydrometer, to improve accuracy over previously using a standard solution with table salt to calibrate an electronic probe aiming for 1.025.

The hydrometer measures 1.028, much higher than I expected. It also says "Recommended range: 1.025 to 1.027 at 77F" which is much higher than I thought anyone would recommend. Below 1.025 is common in fish-only systems and people being cheap, but I've never seen anyone intentionally go higher unless trying to reproduce a Red Sea specific environment.

My tank is 78.6F, which is about the hottest it goes in summer. My heaters kick on at 77F.

Is there a reason both the recommendation and measurement seem high? Should I gradually lower my salinity to 1.025?

 

[Randy Holmes-Farley]

The solution needed to calibrate a hydrometer is VERY different than that for an electronic probe when made using sodium chloride.

I show how to make each of them here:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

 

[Randy Holmes-Farley]

FWIW, a salinity of 35 ppt (matching the world ocean average) represents a specific gravity of 1.0264. I presume that is the basis for their recommended range. That's what I recommend.

 

[BradB]

I've seen that article, and am well aware that hydrometer calibration to natural seawater values would be a different solution than to calibrate a probe. I never had a hydrometer before, so I've never tried to make any calibration fluid except for the probe.

The hydrometer was a $30 purchase. If it is consistent and saves me the time and salt recalibrating my probe once a month (or so), it is well worth $30.

I've always seen 35ppt and 1.025 not 1.0264. I need to be more suspicious of suspiciously round numbers.

 

[arking_mark]

I used the TM Hydrometer to answer my salinity questions. There are online calculors the provide temp adjustment for Hydrometers.

 

[Saltyreef]

Its meant to be floated in 77 degree water.

I remove enough water to float it in a small cylinder.
If your tank runs at 78, it will be cooled to 77 while your taking readings.

The TM hydrometer is the most accurate device on the market for aquarium salinity IMO.
My miluakee is darn close too.

 

[Randy Holmes-Farley]

The TM hydrometer is the most accurate device on the market for aquarium salinity IMO.
My miluakee is darn close too.

It's not more accurate than a good conductivity meter, and much harder to use.

 

[Reef.]

I use a measuring cylinder for mine, my water is slightly higher than the hydrometer calibration temp, time it cools in the glass cylinder it's at temp.

You can either raise your tank temp to accommodate or if using a measuring cylinder, either preheat with a little warm water, if you choose not to raise your tank temp or use a salinity correction calculator.

Salinity Correction Calculator

Aquarium calculator; Correct a relative specific gravity (sg) measurement taken with a non-temperature-correcting unit.

www.hamzasreef.com

 

[Randy Holmes-Farley]

I've seen that article, and am well aware that hydrometer calibration to natural seawater values would be a different solution than to calibrate a probe. I never had a hydrometer before, so I've never tried to make any calibration fluid except for the probe.

The hydrometer was a $30 purchase. If it is consistent and saves me the time and salt recalibrating my probe once a month (or so), it is well worth $30.

I've always seen 35ppt and 1.025 not 1.0264. I need to be more suspicious of suspiciously round numbers.

So are things straightened out now? I'm not seeing an issue...

 

[Saltyreef]

It's not more accurate than a good conductivity meter, and much harder to use.

I have a "good" conductivity meter at work.
It was $1400.
It also requires regular calibration.

Sure it may be easier to stick a probe in the water and read the digital value....
But floating hydrometers have been an industry standard for many measurements and are still in use today because they plain work and dont stop until you drop

 

[driftin]

I use a measuring cylinder for mine, my water is slightly higher than the hydrometer calibration temp, time it cools in the glass cylinder it's at temp.

You can either raise your tank temp to accommodate or if using a measuring cylinder, either preheat with a little warm water, if you choose not to raise your tank temp or use a salinity correction calculator.

Salinity Correction Calculator

Aquarium calculator; Correct a relative specific gravity (sg) measurement taken with a non-temperature-correcting unit.

www.hamzasreef.com

Thanks for the calculator link. I have to ask (and I'm not using one of these hydrometers yet) - is it worth worrying about compensating for the temperature? According to that calculator a temperature difference of 2 degrees F is only a specific gravity difference of 0.003, which is certainly less than the resolution I get looking through my refractometer...

 

[Randy Holmes-Farley]

I have a "good" conductivity meter at work.
It was $1400.
It also requires regular calibration.

Sure it may be easier to stick a probe in the water and read the digital value....
But floating hydrometers have been an industry standard for many measurements and are still in use today because they plain work and dont stop until you drop

Mine (an Orion 128 with 4 electrode probe) never varied in calibration in years (and actually did not permit "calibration").

I'm not saying a floating glass hydrometer is not plenty accurate. I'm disputing that it is not "the most accurate device on the market for aquarium salinity".

I'll bet most people using the Tropic Marin do not ever even check them for accuracy at reef salinity. They just assume it is. I checked mine and it was accurate, but does that mean that every one is perfectly made? I would not assume so.

 

[Reef.]

Thanks for the calculator link. I have to ask (and I'm not using one of these hydrometers yet) - is it worth worrying about compensating for the temperature? According to that calculator a temperature difference of 2 degrees F is only a specific gravity difference of 0.003, which is certainly less than the resolution I get looking through my refractometer...

Good question...in my experience the nearer you are to the hydrometer calibration temp the more accurate the correction calculator is, if it's only a faction of the temp then it's not going to change things much

Worth using for more than a couple of degrees though as the TM measures to 1.0264 you might as well try and hit that mark.

 

[Randy Holmes-Farley]

Thanks for the calculator link. I have to ask (and I'm not using one of these hydrometers yet) - is it worth worrying about compensating for the temperature? According to that calculator a temperature difference of 2 degrees F is only a specific gravity difference of 0.003, which is certainly less than the resolution I get looking through my refractometer...

The good thing about salinity is that a wide range seems quite acceptable to the organisms we keep. For most purposes, a correction of that size is unnecessary.

 

[Reef.]

Mine (an Orion 128 with 4 electrode probe) never varied in calibration in years (and actually did not permit "calibration").

I'm not saying a floating glass hydrometer is not plenty accurate. I'm disputing that it is not "the most accurate device on the market for aquarium salinity".

I'll bet most people using the Tropic Marin do not ever even check them for accuracy at reef salinity. They just assume it is. I checked mine and it was accurate, but does that mean that every one is perfectly made? I would not assume so.

I checked mine but agree most probably don't, but again do those with other devices check theirs or check the calibration fluid they use?

 

[driftin]

Thanks for the replies - and I just noticed I was off with the decimal point in my post above. 2 degrees F is 0.0003, not 0.003. That makes a big difference!