Proper calibration of refractometer? (Am I doing this wrong?)

[fishy_fishy_fish]

Hi everyone,

So I purchased a refractometer and have been trusting it so far. I calibrated it with the RO water I use prior to mixing with salt, had it reach zero on the dot, and then have been making/adding water that reads as 1.026.

This all seems correct to me, but I have seen a few warnings about these readings and having your salinity actually be way off. I’ve also seen people say you have to use a calibration fluid.

I’m not made of money so I’m trying to avoid expensive solutions, but I’m wondering if this is the right way or if I should pivot before adding livestock and corals? It’s a cheaper refractometer from amazon but it was the highest reviewed and most purchased.

Any help is appreciated, thank you!

 

[Fish Fan]

I would suggest that you do not calibrate the refractometer with distilled water, even if the instructions advise you to do so. Better, is to calibrate with a standard solution at the range where you’ll be measuring your seawater. There has been some inconsistency with calibration fluids/standards that are purchased, so I’d suggest making your own 35 ppt standard solution following this guide from Randy Holmes-Farley. It’s quite easy to make using everyday Morton’s Iodized kitchen salt, if you have questions please ask

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/
Good luck!

 

[exnisstech]

Unless your calibrating with a solution of a known salinty there's no way to be 100% certain your readings are accurate unless you have another device to compare to that you know is accurate.

 

[fishy_fishy_fish]

I would suggest that you do not calibrate the refractometer with distilled water, even if the instructions advise you to do so. Better, is to calibrate with a standard solution at the range where you’ll be measuring your seawater. There has been some inconsistency with calibration fluids/standards that are purchased, so I’d suggest making your own 35 ppt standard solution following this guide from Randy Holmes-Farley. It’s quite easy to make using everyday Morton’s Iodized kitchen salt, if you have questions please ask

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/
Good luck!

Unless your calibrating with a solution of a known salinty there's no way to be 100% certain your readings are accurate unless you have another device to compare to that you know is accurate.

Ok, thank you very much. I will follow the guide you attached. It’s very interesting to me how many nuanced aspects of this hobby are missed without the community. Very interested to see how the solution compares to what I’ve been doing so far, considering it’s what the instructions call for. If my salinity is way off that says a lot, so thank you!

 

[Randy Holmes-Farley Verified Community Expert]

Ok, thank you very much. I will follow the guide you attached. It’s very interesting to me how many nuanced aspects of this hobby are missed without the community. Very interested to see how the solution compares to what I’ve been doing so far, considering it’s what the instructions call for. If my salinity is way off that says a lot, so thank you!

What device is it? A true seawater refractometer that is perfectly made and perfectly calibrated will be fine calibrated with ro/di.

A brine refractometer repurposed for hobby use that is
Perfectly made and perfectly calibrated with ro water must give a slightly inaccurate answer.

Any refractometer that is improperly made that is perfectly calibrated with ro water may be significantly off.

Any type of refractometer, perfectly or imperfectly made, will correctly read 35 ppt seawater if calibrated properly with a 35 ppt standard.

 

[BryanM]

I can't answer the question. I gave up on two refracometers and a digital milwakee.

I use a Tropic Marin hydrometer now, which finally match my ICP test results.

 

[fishy_fishy_fish]

What device is it? A true seawater refractometer that is perfectly made and perfectly calibrated will be fine calibrated with ro/di.

A brine refractometer repurposed for hobby use that is
Perfectly made and perfectly calibrated with ro water must give a slightly inaccurate answer.

Any refractometer that is improperly made that is perfectly calibrated with ro water may be significantly off.

Any type of refractometer, perfectly or imperfectly made, will correctly read 35 ppt seawater if calibrated properly with a 35 ppt standard.

I got it from Amazon so I’m thinking the calibration fluid is going to be the most concrete way to get accurate readings.

I can't answer the question. I gave up on two refracometers and a digital milwakee.

I use a Tropic Marin hydrometer now, which finally match my ICP test results.

That’s interesting. How were the incorrect readings affecting your tank?

 

[BryanM]

That’s interesting. How were the incorrect readings affecting your tank?

I think that’s hard to say.

I was consistently getting back 33ppt from the icp tests even tho my testing was at 35.

But I was also dosing afr at the time, so any conclusions I might come up with would really just be guesses.

 

[fishy_fishy_fish]

I think that’s hard to say.

I was consistently getting back 33ppt from the icp tests even tho my testing was at 35.

But I was also dosing afr at the time, so any conclusions I might come up with would really just be guesses.

Fair, but I understand that if you can control something with regards to parameters, you should. Especially if it’s easier like salinity. That’s why I don’t want my refractometer to be misleading, I’d rather “I know it’s not because of this” over “it could be this.”

Will probably use the solution linked and then might invest in a hydrometer to compare.

 

[Randy Holmes-Farley Verified Community Expert]

I got it from Amazon so I’m thinking the calibration fluid is going to be the most concrete way to get accurate readings.

That’s interesting. How were the incorrect readings affecting your tank?

Yes, using a diy or other accurate standard is always a good choice.

 

[fishy_fishy_fish]

Yes, using a diy or other accurate standard is always a good choice.

Unless your calibrating with a solution of a known salinty there's no way to be 100% certain your readings are accurate unless you have another device to compare to that you know is accurate.

Sorry to revive this, but I was just wondering if there is anything special about the Morton’s salt used in that guide? I’m up in Canada so the common option is Windsor, which has both a sea salt and table salt option.

 

[exnisstech]

Sorry to revive this, but I was just wondering if there is anything special about the Morton’s salt used in that guide? I’m up in Canada so the common option is Windsor, which has both a sea salt and table salt option.

@Randy Holmes-Farley

 

[Randy Holmes-Farley Verified Community Expert]

Sorry to revive this, but I was just wondering if there is anything special about the Morton’s salt used in that guide? I’m up in Canada so the common option is Windsor, which has both a sea salt and table salt option.

No, if you go by mass rather than volume for the salt. Use table salt.