Refractometer or salinity tester from Amazon?

[drippyfish]

I just setup a new tank and and got a hydrometer but im not too sure how accurate it is, im not sure if i should get a refractometer or a pawfly 5 in 1 salinity tester from amazon? I would get a Hanna checker but thats not in my budget yet.

 

[TX_REEF]

the amazon made in china brand units are hit or miss on accuracy. If I were you I'd just save up the few extra bucks and spring for the hanna. It's used and trusted by professionals and hobbyists alike for a reason.

 

[RocketEngineer]

To me, that looks like something for swimming pools, not saltwater tanks. A refractometer is a much better way to measure salinity.

 

[Randy Holmes-Farley]

Cannot tell from a picture, but there’s a good chance it cannot read salinity high enough.

 

[Baylott224]

I just setup a new tank and and got a hydrometer but im not too sure how accurate it is, im not sure if i should get a refractometer or a pawfly 5 in 1 salinity tester from amazon? I would get a Hanna checker but thats not in my budget yet.

https://a.co/d/eRHm2s8 is good or go to brs and get a refractometer

 

[EnterName]

For precise and easy measurements: Get a hydrometer. You won't need to calibrate it and as long as it is calibrated for 25°C/77°F you won't need to adjust for temperature (assuming your tank is at that temperature).

For faster measurements and automatic calibration for temperature get a refractometer with automatic temperature compensation (ATC). It should be calibrated with a 35ppt solution to ensure best precision near the expected salinity.

Both are cheap options that offer sufficiently precise measurements and you don't need to worry about degrading electrodes, batteries, etc.

I highly recommend using devices that come with a conversion table or can be used directly to measure the salinity in %, ppt, or g/L as comparing specific gravity measurements between devices isn't as trivial as people think it is. So don't be confused when two devices show different readings, they both are probably correct, but you need to refer to a conversion table specifically designed for your device.

 

[Randy Holmes-Farley]

https://a.co/d/eRHm2s8 is good or go to brs and get a refractometer

It has a pretty wide error window per the manufacturer.

 

[Randy Holmes-Farley]

I highly recommend using devices that come with a conversion table or can be used directly to measure the salinity in %, ppt, or g/L as comparing specific gravity measurements between devices isn't as trivial as people think it is. So don't be confused when two devices show different readings, they both are probably correct, but you need to refer to a conversion table specifically designed for your device.

I’m not sure what you are claiming exactly. Can you give an example of when measured sg is not the same between properly calibrated device types?

 

[tzabor10]

I got a Neptune salinity probe two years ago. It has never worked. A refractometer is a good idea

 

[EnterName]

I highly recommend using devices that come with a conversion table or can be used directly to measure the salinity in %, ppt, or g/L as comparing specific gravity measurements between devices isn't as trivial as people think it is. So don't be confused when two devices show different readings, they both are probably correct, but you need to refer to a conversion table specifically designed for your device.

I’m not sure what you are claiming exactly. Can you give an example of when measured sg is not the same between properly calibrated device types?

There are actually TWO "calibration" temperatures for everything that measures relative density.
First you have the calibration temperature everyone knows about: The temperature at which you need to measure your sample. For most devices for the hobby this is 25°C/77°F or 20°C/68°F.
But now you have to think about what your device is measuring relative to. Fresh water at 25°C/77°F? Fresh water at 20°C/68°F? Fresh water at 4°C/39.2°F where water reaches its densest point?
This actually depends on the device and the standard the manufacturer chose. In theory the manufacturer could make the device yield measurements relative to 100% Ethanol at a certain temperature instead of fresh water (not really happening for devices designed for this hobby but you get the idea).

For example: I have a Hydrometer that measures a sample at 25°C/77°F relative to the manufacturer's standard solution which is fresh water at 4°C. On the hydrometer is a small text saying Sp.Gr. 25/4 to point this out. I also have a refractometer which measures a sample at 20°C/68°F relative to a different manufacturer's standard which is fresh water at 20°C/68°F. If you look through your refractometer you might see a text d20/20 or d68/68 which points this out.

What does this mean for my measurements?
Fresh water is denser at 4°C/39.2°F than at 20°C/68°F. So if I get a reading of for example 1.025 on my hydrometer this would be around 37ppt. But on my Refractometer 1.025 would mean around 35.5ppt. Not an enormous difference, but it can still cause confusion why to devices show different values even though the same sample is measured and the instructions were followed carefully (measured at the devices calibration temperatures so no adjustment is necessary).

I hope this was understandable. Most people seem unaware of this issue as the differences are small and the measuring devices used for the hobby aren't necessarily that precise. But I've read so many people claiming they don't use device X because it showed different values than their newly bought Refractometer/hydrometer/tds meter. Most of them work absolutely fine, but you need to understand that 1.023 on device A might mean something different than on device B and that it has nothing to do with the temperature at which you have to take the measurement.

 

[Reef Jedi]

Pick up a good refractometer and some solution. I check and re calibrate every quarter but I find it really doesn’t need much tuning. I like the Red Sea brand as it’s slightly shorter than some other generic ones. It will last a long time, I picked up a newer one as my last one was about 20 years old.

 

[56longroof]

Neither. Get a Tropic Marin hydrometer. Simple,no calibration,and fairly inexpensive.

 

[Baylott224]

https://a.co/d/eRHm2s8 is good or go to brs and get a refractometer

It has a pretty wide error window per the manufacturer.

I don't know but Ive been using it for a about 7 years now it works well for me. So the tm hydrometer do you hold it with your hand or does it just float.

 

[Boehmtown]

I've had almost all of them. The tropic marin floating hydrometer and a graduated cylinder has been my favorite and most accurate. Hanna pen distant second

 

[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.

 

[ga2040]

Always used refractometer for years , they are pretty reliable as they use simple physics.(no electronics no sensors)

 

[Randy Holmes-Farley]

There are actually TWO "calibration" temperatures for everything that measures relative density.
First you have the calibration temperature everyone knows about: The temperature at which you need to measure your sample. For most devices for the hobby this is 25°C/77°F or 20°C/68°F.
But now you have to think about what your device is measuring relative to. Fresh water at 25°C/77°F? Fresh water at 20°C/68°F? Fresh water at 4°C/39.2°F where water reaches its densest point?
This actually depends on the device and the standard the manufacturer chose. In theory the manufacturer could make the device yield measurements relative to 100% Ethanol at a certain temperature instead of fresh water (not really happening for devices designed for this hobby but you get the idea).

For example: I have a Hydrometer that measures a sample at 25°C/77°F relative to the manufacturer's standard solution which is fresh water at 4°C. On the hydrometer is a small text saying Sp.Gr. 25/4 to point this out. I also have a refractometer which measures a sample at 20°C/68°F relative to a different manufacturer's standard which is fresh water at 20°C/68°F. If you look through your refractometer you might see a text d20/20 or d68/68 which points this out.

What does this mean for my measurements?
Fresh water is denser at 4°C/39.2°F than at 20°C/68°F. So if I get a reading of for example 1.025 on my hydrometer this would be around 37ppt. But on my Refractometer 1.025 would mean around 35.5ppt. Not an enormous difference, but it can still cause confusion why to devices show different values even though the same sample is measured and the instructions were followed carefully (measured at the devices calibration temperatures so no adjustment is necessary).

I hope this was understandable. Most people seem unaware of this issue as the differences are small and the measuring devices used for the hobby aren't necessarily that precise. But I've read so many people claiming they don't use device X because it showed different values than their newly bought Refractometer/hydrometer/tds meter. Most of them work absolutely fine, but you need to understand that 1.023 on device A might mean something different than on device B and that it has nothing to do with the temperature at which you have to take the measurement.

Thanks.

I am aware of the variety of issues and complications around measurement and comparison temps for hydrometers and have a detailed article on it. It’s not so much of an issue for refractometers or conductivity meters as those generally correct themselves electronically or mechanically.

Chemistry and the Aquarium: Specific Gravity: Oh How Complicated!

This month, Randy explains and reviews specific gravity.

reefs.com

But specific gravity (as opposed to a hydrometer reading) is typically defined as the density of the fluid divided by the density of pure water at the same temp, and it does not change very much with temperature unless one makes big temp changes.

It was your mention of different devices that was throwing me. I’d be wary of using the sort of ppt conversion tables you mention for unusual hydrometers (say, the 25/4 you mention) since the conversion may not be generated for seawater.

 

[Randy Holmes-Farley]

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

 

[Randy Holmes-Farley]

I don't know but Ive been using it for a about 7 years now it works well for me. So the tm hydrometer do you hold it with your hand or does it just float.

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.

 

[EnterName]

There are actually TWO "calibration" temperatures for everything that measures relative density.
First you have the calibration temperature everyone knows about: The temperature at which you need to measure your sample. For most devices for the hobby this is 25°C/77°F or 20°C/68°F.
But now you have to think about what your device is measuring relative to. Fresh water at 25°C/77°F? Fresh water at 20°C/68°F? Fresh water at 4°C/39.2°F where water reaches its densest point?
This actually depends on the device and the standard the manufacturer chose. In theory the manufacturer could make the device yield measurements relative to 100% Ethanol at a certain temperature instead of fresh water (not really happening for devices designed for this hobby but you get the idea).

For example: I have a Hydrometer that measures a sample at 25°C/77°F relative to the manufacturer's standard solution which is fresh water at 4°C. On the hydrometer is a small text saying Sp.Gr. 25/4 to point this out. I also have a refractometer which measures a sample at 20°C/68°F relative to a different manufacturer's standard which is fresh water at 20°C/68°F. If you look through your refractometer you might see a text d20/20 or d68/68 which points this out.

What does this mean for my measurements?
Fresh water is denser at 4°C/39.2°F than at 20°C/68°F. So if I get a reading of for example 1.025 on my hydrometer this would be around 37ppt. But on my Refractometer 1.025 would mean around 35.5ppt. Not an enormous difference, but it can still cause confusion why to devices show different values even though the same sample is measured and the instructions were followed carefully (measured at the devices calibration temperatures so no adjustment is necessary).

I hope this was understandable. Most people seem unaware of this issue as the differences are small and the measuring devices used for the hobby aren't necessarily that precise. But I've read so many people claiming they don't use device X because it showed different values than their newly bought Refractometer/hydrometer/tds meter. Most of them work absolutely fine, but you need to understand that 1.023 on device A might mean something different than on device B and that it has nothing to do with the temperature at which you have to take the measurement.

Thanks.

I am aware of the variety of issues and complications around measurement and comparison temps for hydrometers and have a detailed article on it. It’s not so much of an issue for refractometers or conductivity meters as those generally correct themselves electronically or mechanically.

Chemistry and the Aquarium: Specific Gravity: Oh How Complicated!

This month, Randy explains and reviews specific gravity.

reefs.com

But specific gravity (as opposed to a hydrometer reading) is typically defined as the density of the fluid divided by the density of pure water at the same temp, and it does not change very much with temperature unless one makes big temp changes.

It was your mention of different devices that was throwing me. I’d be wary of using the sort of ppt conversion tables you mention for unusual hydrometers (say, the 25/4 you mention) since the conversion may not be generated for seawater.

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.