Refractometer or salinity tester from Amazon?

[Randy Holmes-Farley]

No problem!

Yes, for hydrometers with ATC and for pretty much all conductivity meters I know of, you don't need to adjust for temperature yourself which makes their use a bit easier besides needing regular calibration.

And you are right, most devices have equal calibration and reference temperatures but if two such devices have different calibration/reference temperatures their readings will still be slightly different of course.

I have written some code that can generate these conversion tables for all reference temperatures between like 1°C and 38°C or so to a very small standard error (don't remember the exact numbers by heart, but within useful ranges for reef tanks). It's specifically designed for seawater based on scientific papers/journals that are well known and are being used for pretty much all these conversion tables, so I can verify that the tables for the JBL Hydrometer (6140800) I was talking about are fine.

25/4 sounds weird but it makes sense as reef tanks are often kept at 25°C/77°F and water is near its densest point at 4°C/39.2°F under standard pressure as your very nice article points out as well. It's very close to 1kg/L = 1kg/dm³ = 1g/cm³ so measurements are near their "absolute" density this way.

I don’t agree that this is a significant issue for reefers to worry about using any of the hydrometers reefers normally employ. I note the actual gravity differences in the above article. Only the rarely used 4/4 has enough deviation to matter at all.

For example, the specific gravity of natural seawater (S =35) is 1.0278 using the 3.98 °C standard, 1.0269 using the 60 °F standard, 1.0266 using the 20 °C standard, and 1.0264 using the 77 °F standard.

 

[Mr. Mojo Rising]

I've used both refractometers and hydrometers, frankly I prefer the hanna tester. Its more expensive, but to me the simplicity, accuracy, and speed of the device make it worth the extra money. IMO

 

[EnterName]

No problem!

Yes, for hydrometers with ATC and for pretty much all conductivity meters I know of, you don't need to adjust for temperature yourself which makes their use a bit easier besides needing regular calibration.

And you are right, most devices have equal calibration and reference temperatures but if two such devices have different calibration/reference temperatures their readings will still be slightly different of course.

I have written some code that can generate these conversion tables for all reference temperatures between like 1°C and 38°C or so to a very small standard error (don't remember the exact numbers by heart, but within useful ranges for reef tanks). It's specifically designed for seawater based on scientific papers/journals that are well known and are being used for pretty much all these conversion tables, so I can verify that the tables for the JBL Hydrometer (6140800) I was talking about are fine.

25/4 sounds weird but it makes sense as reef tanks are often kept at 25°C/77°F and water is near its densest point at 4°C/39.2°F under standard pressure as your very nice article points out as well. It's very close to 1kg/L = 1kg/dm³ = 1g/cm³ so measurements are near their "absolute" density this way.

I don’t agree that this is a significant issue for reefers to worry about using any of the hydrometers reefers normally employ. I note the actual gravity differences in the above article. Only the rarely used 4/4 has enough deviation to matter at all.

For example, the specific gravity of natural seawater (S =35) is 1.0278 using the 3.98 °C standard, 1.0269 using the 60 °F standard, 1.0266 using the 20 °C standard, and 1.0264 using the 77 °F standard.

The difference is negligible between the common 20/20 and 25/25 that's absolutely correct. For the 15.6 (60°F standard) there would be roughly 0.5ppt difference, so no big deal either.

For 25/4 hydrometers which can be bought from for example JBL and AquaMedic (they also have a 25/4 refractometer as it seems), the difference becomes noticable.

For example:
37.2ppt would show 1.025 on a 25/4 standard. But it would read 1.028 on a 25/25.
33.2ppt would show 1.022 on a 25/4 standard.
But it would read 1.025 on a 25/25.

Here is a online calculator that can be used to double check:

Salinity Conversion Calculator — Capital City Aquatics

This calculator converts Salinity from Specific Gravity (SG) to Parts Per Trillion (ppt) and others. Best Salinity Converter!

www.capitalcityaquatics.com

This difference only becomes a problem when a person is trying to verify their readings with a different device (with a different standard), or is wondering why someone is calling "1.025" elevated salinity even though it's only 33ppt according to their own (25/25) device.
The difference of roughly 4ppt won't cause harm to fish or corals if someone doesn't purposely targets very high or very low salinity and confuses the conversion tables between the two extremes 25/25 and 25/4. This part is a non-issue just as you said.

 

[get-salty]

I got a refractometer from Amazon 5 yrs ago and still using it. I calibrate it with RO and with calibration fluid and it is bang on for the last 5 yrs.

Pick which type of instrument you want and stick with it most importantly.. you have to be consistent, thats all that matters.

 

[56longroof]

It’s a floating glass hydrometer.

It’s a fine device, but has real use limitations that make a good conductivity meter a much better bet for me.

What do you consider its use limitations?

 

[penfold2]

What do you consider its use limitations?

It requires a 12" water depth. I have one and love it, but I can't use it to test my 25g tank because it hits the bottom of the tank. Can't use it to test bag water from vendors either. I love the precision and no calibration, but there are times I need a refractometer. I basically use the hydrometer to test my new saltwater and then calibrate my refractometer accordingly.

 

[Randy Holmes-Farley]

What do you consider its use limitations?

Not easy to use in acclimation of incoming organisms. Not easy to use making a batch of new salt water. Lacks other uses a conductivity meter has such as kalk potency.

A drop in corded conductivity probe and meter combo is super easy in these situations.

 

[Randy Holmes-Farley]

The difference is negligible between the common 20/20 and 25/25 that's absolutely correct. For the 15.6 (60°F standard) there would be roughly 0.5ppt difference, so no big deal either.

For 25/4 hydrometers which can be bought from for example JBL and AquaMedic (they also have a 25/4 refractometer as it seems), the difference becomes noticable.

For example:
37.2ppt would show 1.025 on a 25/4 standard. But it would read 1.028 on a 25/25.
33.2ppt would show 1.022 on a 25/4 standard.
But it would read 1.025 on a 25/25.

Here is a online calculator that can be used to double check:

Salinity Conversion Calculator — Capital City Aquatics

This calculator converts Salinity from Specific Gravity (SG) to Parts Per Trillion (ppt) and others. Best Salinity Converter!

www.capitalcityaquatics.com

This difference only becomes a problem when a person is trying to verify their readings with a different device (with a different standard), or is wondering why someone is calling "1.025" elevated salinity even though it's only 33ppt according to their own (25/25) device.
The difference of roughly 4ppt won't cause harm to fish or corals if someone doesn't purposely targets very high or very low salinity and confuses the conversion tables between the two extremes 25/25 and 25/4. This part is a non-issue just as you said.

I haven’t looked at the jbl yet, but the aqua medic seems to actually read in density, not specific gravity, unless they think sg has units. That is a big difference and I think such a device is too confusing for most reefers to use.

Aqua Medic DensiMeter | Aqua Medic Hydrometer | Measure & control

Aqua Medic DensiMeter Hydrometer to determine the density [g / ml] Tp. 25/4 ° C in saltwater aquariums. Let the hydrometer float freely in sufficiently deep water

reef-aquarium-store.com

 

[56longroof]

It requires a 12" water depth. I have one and love it, but I can't use it to test my 25g tank because it hits the bottom of the tank. Can't use it to test bag water from vendors either. I love the precision and no calibration, but there are times I need a refractometer. I basically use the hydrometer to test my new saltwater and then calibrate my refractometer accordingly.

I have a swing arm hydrometer I can use for quick checks. I used the TM to "calibrate" it. 1.022 is 1.0255 on the one I have. With those 2 basic tools I have my needs covered.

 

[56longroof]

Not easy to use in acclimation of incoming organisms. Not easy to use making a batch of new salt water. Lacks other uses a conductivity meter has such as kalk potency.

A drop in corded conductivity probe and meter combo is super easy in these situations.

I never test vendor water. In fact most times I dont even drip acclimate anymore. Just temp and that's it. I use mine for new batches but I make 50 gallons at a time. For quick checks a calibrated swing arm serves me well. But that's just my needs. Everyone has different methods.

 

[EnterName]

The difference is negligible between the common 20/20 and 25/25 that's absolutely correct. For the 15.6 (60°F standard) there would be roughly 0.5ppt difference, so no big deal either.

For 25/4 hydrometers which can be bought from for example JBL and AquaMedic (they also have a 25/4 refractometer as it seems), the difference becomes noticable.

For example:
37.2ppt would show 1.025 on a 25/4 standard. But it would read 1.028 on a 25/25.
33.2ppt would show 1.022 on a 25/4 standard.
But it would read 1.025 on a 25/25.

Here is a online calculator that can be used to double check:

Salinity Conversion Calculator — Capital City Aquatics

This calculator converts Salinity from Specific Gravity (SG) to Parts Per Trillion (ppt) and others. Best Salinity Converter!

www.capitalcityaquatics.com

This difference only becomes a problem when a person is trying to verify their readings with a different device (with a different standard), or is wondering why someone is calling "1.025" elevated salinity even though it's only 33ppt according to their own (25/25) device.
The difference of roughly 4ppt won't cause harm to fish or corals if someone doesn't purposely targets very high or very low salinity and confuses the conversion tables between the two extremes 25/25 and 25/4. This part is a non-issue just as you said.

I haven’t looked at the jbl yet, but the aqua medic seems to actually read in density, not specific gravity. That is a big difference and I think such a device is too confusing for most reefers to use.

Aqua Medic DensiMeter | Aqua Medic Hydrometer | Measure & control

Aqua Medic DensiMeter Hydrometer to determine the density [g / ml] Tp. 25/4 ° C in saltwater aquariums. Let the hydrometer float freely in sufficiently deep water

reef-aquarium-store.com

Specific gravity measured with the 4°C standard is equal to density because at 4°C (assuming standard pressure) water has a density of 1g/ml.
If you measure relative to "1" your readings will always be equal to the absolute value.

That's why the 4°C standard is so commonly used in scientific measuring devices. You don't need to convert your readings from specific gravity/relative density to density. You can simply pretend that the device measures density and the readings will be correct.

It's the same for the JBL. Both still measure specific gravity/relative density. But they chose a smart standard so you directly have the density as well. There is no difference in the use or how you convert measurements to ppt. You simply use the correct conversion table as you would with 25/25, 20/20, etc. devices.

 

[Randy Holmes-Farley]

Specific gravity measured with the 4°C standard is equal to density because at 4°C (assuming standard pressure) water has a density of 1g/ml.
If you measure relative to "1" your readings will always be equal to the absolute value.

That's why the 4°C standard is so commonly used in scientific measuring devices. You don't need to convert your readings from specific gravity/relative density to density. You can simply pretend that the device measures density and the readings will be correct.

It's the same for the JBL. Both still measure specific gravity/relative density. But they chose a smart standard so you directly have the density as well. There is no difference in the use or how you convert measurements to ppt. You simply use the correct conversion table as you would with 25/25, 20/20, etc. devices.

Ok, I understand what you are suggesting about this device giving data that is not equivalent since it is giving density. I personally would not recommend that reefers use it but instead just use a device that gives more standard units of measure for salinity or specific gravity. :)

 

[EnterName]

Specific gravity measured with the 4°C standard is equal to density because at 4°C (assuming standard pressure) water has a density of 1g/ml.
If you measure relative to "1" your readings will always be equal to the absolute value.

That's why the 4°C standard is so commonly used in scientific measuring devices. You don't need to convert your readings from specific gravity/relative density to density. You can simply pretend that the device measures density and the readings will be correct.

It's the same for the JBL. Both still measure specific gravity/relative density. But they chose a smart standard so you directly have the density as well. There is no difference in the use or how you convert measurements to ppt. You simply use the correct conversion table as you would with 25/25, 20/20, etc. devices.

Ok, I understand what you are suggesting about this device giving data that is not equivalent since it is giving density. I personally would not recommend that reefers use it but instead just use a device that gives more standard units of measure for salinity or specific gravity. :)

The difference to the more common 25/25 standard is still roughly 4ppt as we discussed earlier, so it's small, but noticable.

I personally prefer 25/4 or 20/4 as it reduces the difference between specific gravity and density to zero (it still is specific gravity though!). This way people wouldn't really need to understand the concept of specific gravity in the first place.
I don't know why this hasn't become the established standard to be honest.

But of course I fully understand why you cannot recommend using devices that differ noticeably from the standards that are more commonly used in this hobby even though they measure the same thing.

Converting readings into meaningful absolute units such as ppt solves all these issues, so I decided for myself to stop using specific gravity and instead talk about salinity in ppt, g/kg, g/L, etc.

 

[Randy Holmes-Farley]

The difference to the more common 25/25 standard is still roughly 4ppt as we discussed earlier, so it's small, but noticable.

I personally prefer 25/4 or 20/4 as it reduces the difference between specific gravity and density to zero (it still is specific gravity though!). This way people wouldn't really need to understand the concept of specific gravity in the first place.
I don't know why this hasn't become the established standard to be honest.

But of course I fully understand why you cannot recommend using devices that differ noticeably from the standards that are more commonly used in this hobby even though they measure the same thing.

Converting readings into meaningful absolute units such as ppt solves all these issues, so I decided for myself to stop using specific gravity and instead talk about salinity in ppt, g/kg, g/L, etc.

I agree that converting into ppt will solve any misunderstandings when using a device that reads density instead of specific gravity, but that is, IMO, unnecessarily complicated for the average reefer. They already have to worry about measurement temperature effects on floating glass hydrometers.

I think using a device that directly gives readily comparable readings to what others report is a better plan for most people. :)

 

[EnterName]

The difference to the more common 25/25 standard is still roughly 4ppt as we discussed earlier, so it's small, but noticable.

I personally prefer 25/4 or 20/4 as it reduces the difference between specific gravity and density to zero (it still is specific gravity though!). This way people wouldn't really need to understand the concept of specific gravity in the first place.
I don't know why this hasn't become the established standard to be honest.

But of course I fully understand why you cannot recommend using devices that differ noticeably from the standards that are more commonly used in this hobby even though they measure the same thing.

Converting readings into meaningful absolute units such as ppt solves all these issues, so I decided for myself to stop using specific gravity and instead talk about salinity in ppt, g/kg, g/L, etc.

I agree that converting into ppt will solve any misunderstandings when using a device that reads density instead of specific gravity, but that is, IMO, unnecessarily complicated for the average reefer. They already have to worry about measurement temperature effects on floating glass hydrometers.

I think using a device that directly gives readily comparable readings to what others report is a better plan for most people. :)

That's fair!

Thank you very much for your time and your contributions to the community. I hope I get the chance to give back even a fraction of what you share here.

Maybe I'll come across some interesting research topics I can contribute to with the tools I have available. At the very least I should be able to provide some quality DIC microscopy images for everyone to use once my camera adapter is ready.

Enjoy your day! :)

 

[Baylott224]

For sg the Milwaukee has a +- of. .0001
For psu and ppt it's +-2

The tm hydrometer is +-. 0001 too. yeah I agree the error for psu and ppt is high on the Milwaukee but the sg has the same deviation as the the tm.

That’s not correct. The Milwaukee error is much larger than you state:

The error of the Milwaukee MA 887 (per the manufacturer) is

Accuracy: ±2 PSU | ±2 ppt | ±0.002 S.G. (20/20) | ±0.3°C / ±0.5°F

Your right I'm sorry about the accuracy.

 

[Baylott224]

But I still like it compared to a regular refractometer