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