Glass Hydrometer (Am I Old School)

[alton]

Glass Hydrometers, am I old school or just old? My first tank in 1980 I used a glass hydrometer, so that’s what I am comfortable with. Starting out in the ninety’s I read about refractometers that where not calibrated correctly and people having issues so I did not change. Then I tried the swing arm style, but found out after a year they became liars. Then I found one from Tropic Marin, bought it from Louis at Elegant Reef. It is very similar to the original one I had and ten times better than the glass ones most stores sell.

I have had it forever I am guessing longer than five years not over ten. I realized I needed a backup or maybe a replacement for my old hydrometer. After many visits to different stores coming up empty I ran into the Tropic Marin rep at Macna and he sent two to Terry at Saltyfish Aquariums directly passing up the distributor (since they refused to carry it). Even though it is old, it turns out there is nothing wrong. There is a slight difference between all three but since it is only a .001 to .002 from three hydrometers I feel I am safe, especially since I normally just get it close and go. I was amazed and will send a question why my old one is highlighted from 22 to 25 and the new one highlights 25 to 27?

 

[lickyricky]

IMO a refractometer is the way to go and always provides accurate results. It's very easy to calibrate and only takes a few drops of RO. Place the RO on the reading area and then use the small screwdriver (provided with most) to ensure it is reading a 0 SG/PPM. Then a few drops of tank water and your are in business!

 

[Cjp63]

The tropic marin hydrometer is super accurate. I would not switch they work great.

 

[saltyfilmfolks]

Oh that IS cool!
Unfortunately I don't think there is a TM forum or user here to ask that question of if it's a specific use.

But 26 is 35 pp

https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php

 

[erk]

IMO a refractometer is the way to go and always provides accurate results. It's very easy to calibrate and only takes a few drops of RO. Place the RO on the reading area and then use the small screwdriver (provided with most) to ensure it is reading a 0 SG/PPM. Then a few drops of tank water and your are in business!

This is the incorrect way to calibrate a refractometer. I believe @Randy Holmes-Farley has written an article discussing the correct way to calibrate a refractometer.

As for the hydrometers, if they were calibrated before leaving the factory, they should be far more accurate than a refractometer.

Refractometers, especially digital refractometers, are only more precise since they usually give a number with more significant digits. This is the whole discussion about accuracy and precision. I would stick with the hydrometers.

 

[Randy Holmes-Farley]

There is a slight difference between all three but since it is only a .001 to .002 from three hydrometers I feel I am safe, especially since I normally just get it close and go. I was amazed and will send a question why my old one is highlighted from 22 to 25 and the new one highlights 25 to 27?

Recommended levels for reefs have risen over the years, and many fish only people still aim for the range in the lower one.

FWIW, I think in part, some of the early authors may have confused density with specific gravity, and so thought they were recommending 35 ppt seawater salinity at 1.025 (20 deg C, this is the actual density) while the specific gravity of that sample is really closer to 1.027 at 20 deg C.

 

[Randy Holmes-Farley]

IMO a refractometer is the way to go and always provides accurate results. It's very easy to calibrate and only takes a few drops of RO. Place the RO on the reading area and then use the small screwdriver (provided with most) to ensure it is reading a 0 SG/PPM. Then a few drops of tank water and your are in business!

That's only completely accurate if it is a true seawater refractometer, which many are not. Many are made for sodium chloride solutions, and will give slightly off readings calibrated that way, if used to measure seawater.

For all of them, calibration with a 35 ppt standard will at least give accurate readings for 35 ppt seawater.

 

[Greybeard]

When I first started with a refractometer, I used to test it against my 'old school' glass hydrometer. Haven't done so in years. What's the point? Refractometer, calibrated incorrectly, apparently, by setting RO/DI water to zero, _always_ matches the hydrometer, or close enough not to matter any to me, anyway.

 

[erk]

When I first started with a refractometer, I used to test it against my 'old school' glass hydrometer. Haven't done so in years. What's the point? Refractometer, calibrated incorrectly, apparently, by setting RO/DI water to zero, _always_ matches the hydrometer, or close enough not to matter any to me, anyway.

I used to only calibrate with RO/DI water as well. When I finally calibrated to a 35ppt standard, I found my refractometer was pretty far off. The water I was mixing was higher than I actually thought it was and causing the tank salinity to steadily drift higher. My refractometer was a cheap one off of Amazon, so maybe that is why it was far off. Either way, if I can reduce uncertainties, it will make it far easier to identify the source of a problem when I inevitably have one.

 

[alton]

Recommended levels for reefs have risen over the years, and many fish only people still aim for the range in the lower one.

FWIW, I think in part, some of the early authors may have confused density with specific gravity, and so thought they were recommending 35 ppt seawater salinity at 1.025 (20 deg C, this is the actual density) while the specific gravity of that sample is really closer to 1.027 at 20 deg C.

So after all these years of keeping my tanks at 1.0245 to 1.025 is there a benefit / or a need to slowly bump it up to 1.027 ?

 

[Randy Holmes-Farley]

When I first started with a refractometer, I used to test it against my 'old school' glass hydrometer. Haven't done so in years. What's the point? Refractometer, calibrated incorrectly, apparently, by setting RO/DI water to zero, _always_ matches the hydrometer, or close enough not to matter any to me, anyway.

http://dilbert.com/strip/2008-05-07

 

[Randy Holmes-Farley]

So after all these years of keeping my tanks at 1.0245 to 1.025 is there a benefit / or a need to slowly bump it up to 1.027 ?

Probably not, as reef tanks seem very forgiving of salinity, except you might need less dosing of alk, calcium and magnesium to attain or maintain adequate levels.

 

[Mindi]

I use a modest refractometer and calibrate it to S=35 with a few drops of oceanic NSW every time I use it. I let it stand to temperature adjust for 2-3 minutes first....Takes no time at all and while my S=35 may or may not be "true", I know my tank is same salinity as offshore NSW.

 

[Randy Holmes-Farley]

I use a modest refractometer and calibrate it to S=35 with a few drops of oceanic NSW every time I use it. I let it stand to temperature adjust for 2-3 minutes first....Takes no time at all and while my S=35 may or may not be "true", I know my tank is same salinity as offshore NSW.

It likely is not 35 ppt, but at least it is constant.

 

[Falcon53]

So @Randy Holmes-Farley , given that these Tropic Marin hydrometers can be acquired for $40, is it worth spending $150 on a used Orion 105A+ as we discussed in another thread? Assuming we just want accurate and repeatable measurements of salinity. I'm using the Milwaukee Digital Refractometer currently, and every time I press the read button it gives me a different number, although usually within 0.001 or 0.002.

It appears TM has two versions, one being "high precision." Is the high precision one worth more money?

 

[Randy Holmes-Farley]

So @Randy Holmes-Farley , given that these Tropic Marin hydrometers can be acquired for $40, is it worth spending $150 on a used Orion 105A+ as we discussed in another thread? Assuming we just want accurate and repeatable measurements of salinity. I'm using the Milwaukee Digital Refractometer currently, and every time I press the read button it gives me a different number, although usually within 0.001 or 0.002.

It appears TM has two versions, one being "high precision." Is the high precision one worth more money?

Both are good.

If all you want it for is measuring aquarium salinity (or new salt water salinity), a TM floating glass hydrometer is plenty, but may be less convenient than the conductivity meters, especially if you make new salt water at temps different from the 77 that these are usually calibrated for. You'll need to convert every reading back to 77 with a table.

I tested several hydrometers here, including the normal Tropic Marin which I used for a number of years before I eventually broke it.

Chemistry and the Aquarium: Specific Gravity: Oh How Complicated! ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/2002/1/chemistry

from it:

So how do these hydrometers measure up? In my tank the water was measured to be S=35 ± 0.5 by conductivity. Using the Deep Six swing arm hydrometer I got readings of S=32.5 ± 0.5 at 81 °F and S=32 ± 0.5 at 68 °F. Using the SeaTest I got S=34.5 ± 0.5 at 81 °F and S=34 ± 0.5 at 68 °F. For the standard type Tropic Marin hydrometer, I got a 77 °F/ 77 °F specific gravity of about 1.0265 ± 0.0003 (Figure 4), which compares well to the expected value of 1.0264.

Figure 4. A Tropic Marin hydrometer showing the meniscus rising to about 1.0260, but the actual reading is about 1.0265.