Salinity tester

[Alfredomeinhardt]

I use a refractometer to measure the salinity of my saltwater tank and it always showed 35PPT.

I always calibrated it before I take a measure to make sure the reading is accurate .

I recently ran an ICP test and it came back with a salinity of 32 PPT while my refractometer kept showing 35 PPT

I decided to buy a recently Hannah salinity tester and when I test the tank with it, it showed 32PPT.

Any idea why the difference between the refractometer and the Hana checker?

 

[TokenReefer]

It's just 3 ppt off then I guess, no?

 

[TokenReefer]

Measure to 38 with it

 

[Fish Fan]

Maybe @Randy Holmes-Farley could help if he has a minute to take look.

For now, I would suggest a couple of things. At least some (including myself) have found those Hanna salinity pens to be unreliable, though in my case I admit I purchased mine second hand, so there is that.

I would take a look at this guide from Randy on salinity testers and how to make your own DIY calibration solution, and use this to calibrate your device to 35 ppt. He discusses refractometers and other devices like the Hanna pen. You can make it practically for free using regular Morton's kitchen salt and a decent kitchen scale or measuring spoons:
https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

I hope this helps and good luck!

 

[Alfredomeinhardt]

Maybe @Randy Holmes-Farley could help if he has a minute to take look.

For now, I would suggest a couple of things. At least some (including myself) have found those Hanna salinity pens to be unreliable, though in my case I admit I purchased mine second hand, so there is that.

I would take a look at this guide from Randy on salinity testers and how to make your own DIY calibration solution, and use this to calibrate your device to 35 ppt. He discusses refractometers and other devices like the Hanna pen. You can make it practically for free using regular Morton's kitchen salt and a decent kitchen scale or measuring spoons:
https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

I hope this helps and good luck!

The thing is that the Hanna pen showed the same salinity than my ICP, which led me to think that the one that is off is the refractometer

 

[reefsandfish]

Temperature is what comes to mind for me regarding the refractometer because they are sensitive to that. I keep my calibration solution bottle in the tank to match the tank water temperature before I test it.

 

[Fish Fan]

The thing is that the Hanna pen showed the same salinity than my ICP, which led me to think that the one that is off is the refractometer

It well could be, and the solution you're using to calibrate may be off, that's been noted by other members. Even using RODI water isn't a good idea, even if the device's instructions tell you to do so. Making your own test solution using Randy's recipe will ensure you're refractometer is properly calibrated. Then, compare the refractometer to the Hanna and the ICP.

Here's the nuts and bolts for a refractometer:

"1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1 teaspoon of salt (making about 79.3 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified fresh water (about 2104.4 g)
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container."

That's seriously all you have to do, you probably have everything you need in your kitchen right now

 

[Randy Holmes-Farley Verified Community Expert]

I agree that a cheap refractometer calibrated with ro/di can easily be off.

 

[LeftyReefer]

I don't have much interest in making over 2L of calibration solution in order to use just 3 drops of it to check my refractometer. that seems like a giant waste of both salt and water.

Any way we can have this recipe pared down a bit?
I would think 1/4 Liter (250ml) seems way more reasonable an amount.

79.3g salt into 2104ml water is what the above recipe calls for and will yield over 2L of solution.
if I divide the 2104ml by 250ml, I get 8.416.
divide 79.3g by 8.416 and I get 9.42g.

So if my math isn't off terribly, I could add 9.42g of salt, added to .25L (250ml) water, should yield about the same solution, correct?

Also, the recipe posted above calls for the salt to be added to "purified fresh water".....
I assume RO/DI ok for this?

 

[Gumbies R Us]

I would always double-check the calibration of your cheap refractometer

 

[Randy Holmes-Farley Verified Community Expert]

I don't have much interest in making over 2L of calibration solution in order to use just 3 drops of it to check my refractometer. that seems like a giant waste of both salt and water.

Any way we can have this recipe pared down a bit?
I would think 1/4 Liter (250ml) seems way more reasonable an amount.

79.3g salt into 2104ml water is what the above recipe calls for and will yield over 2L of solution.
if I divide the 2104ml by 250ml, I get 8.416.
divide 79.3g by 8.416 and I get 9.42g.

So if my math isn't off terribly, I could add 9.42g of salt, added to .25L (250ml) water, should yield about the same solution, correct?

Also, the recipe posted above calls for the salt to be added to "purified fresh water".....
I assume RO/DI ok for this?

Yes, one can scale the recipe to any volume you want. For some devices, such as hydrometers (a slightly different recipe) large volumes are needed.

That said, 2 L probably costs less than 50 cents. The large scale minimizes errors with many scales. Doesn't seem a giant waste. lol

Any type of pure water is fine. RO/DI is perfect, but distilled or even many locations tap water is fine.

 

[Mr. Mojo Rising]

Personally I love my hanna tester and my tanks will live and die according to that tester.

 

[LeftyReefer]

Personally I love my hanna tester and my tanks will live and die according to that tester.

Me too. I'd trust my hanna salinity tester over my cheap refractometer any day of the week and twice on sunday. I've had one for almost 4 years and just recently bought a second one, for dedicated use in my QT setup. no more worrying about cross contamination.

First thing I did was compare my old one to the new one and 9 out of 10 times, they give identical results down to the 10th of a degree. and salinity always matches too, once both pens have allowed the temp to stabilize they always give matching readings.

I sent off 2 ICP tests back when I was using a refractometer as my main (only) means of salinity testing. Both ICP tests said my salinity was lower than what I thought it was.
Since switching to the Hanna tester, my ICP salinity results have matched what I thought it was. So at least for me, my Hanna testers have proven to be more accurate than my cheapo refractometer ever was.