Refractometer Calibration

[JBendel]

FWIW:

I must have been asleep in class on this one, but have been calibrating my refractometer with distilled water. After calibrating it with a 35 ppt cal solution (thank you Dong!), my 1.027 salinity was really 1.022 (crosschecked with my brewing Hydrometer).


per google AI:

No, fresh water and saltwater should not be used to calibrate a refractometer the same way; you should always calibrate a refractometer using a saltwater calibration solution for accurate salinity readings, as calibrating with fresh water can lead to inaccurate results, especially when measuring higher salinity levels.

 

[SteveDola]

Just be careful bc the salinity solution can evaporate and change once opened.

I usually take my water every couple of months to a LFS with a Milwaukee salinity meter to verify my readings but then youre relying on the LFS to calibrate their instruments.

 

[danielm5]

FWIW:

I must have been asleep in class on this one, but have been calibrating my refractometer with distilled water. After calibrating it with a 35 ppt cal solution (thank you Dong!), my 1.027 salinity was really 1.022 (crosschecked with my brewing Hydrometer).


per google AI:

No, fresh water and saltwater should not be used to calibrate a refractometer the same way; you should always calibrate a refractometer using a saltwater calibration solution for accurate salinity readings, as calibrating with fresh water can lead to inaccurate results, especially when measuring higher salinity levels.

Another thing I've realized is that since all my measurements are around 35ppt, it's much better to calibrate with 35ppt solution rather than at 0ppt. If I calibrate at 0 salinity, then when measuring around 35ppt my instrument isn't very precise (maybe other refractometers are better but mine is cheap).

 

[Chris.Reef]

Always review the manual that come with your refractometer, hydrometer, etc. For example I use a Veegee stx-3 and for that particular model they say use distilled water for calibration. I also have a Tropic Marin hydrometer to double check readings. Its always a good idea to use at least 2 devises to cross check.

 

[JBendel]

I plan to pick up one of those instant ocean hydrometers for quick cross checks (can't find my old one). If kept clean, probably as accurate as required.

 

[Cooper2]

I plan to pick up one of those instant ocean hydrometers for quick cross checks (can't find my old one). If kept clean, probably as accurate as required.

Cheap instruments aren't worth the price even when free. Get a Hanna tester and back it up with a known good refractometer until it earns your trust. The instant ocean hydrometer stands alone as one of the worst units I've ever used. Had 3 that never agreed with each other and varied wildly. I bought them in my Petco days when new to the hobby and didn't know better.

 

[TPhan]

Cheap instruments aren't worth the price even when free. Get a Hanna tester and back it up with a known good refractometer until it earns your trust. The instant ocean hydrometer stands alone as one of the worst units I've ever used. Had 3 that never agreed with each other and varied wildly. I bought them in my Petco days when new to the hobby and didn't know better.

I agreed, i bought one when i first started and tossed it. Also had a problem with 2 bottles of 35pt calibration fluid. My go to now is the tropic marin hydrometer to keep my refractometer in check.

 

[Joe Rice]

Tropic Marine Hydrometer is the best way to calibrate your refractometer. Very accurate and very precise. Getting a large graduated cylinder makes it easier too.

High Precision Hydrometer

Ensure that your equipment is reading correctly and your aquarium is at the right salinity with Tropic Marin's High Precision Hydrometer. Many tank inhabitants are sensitive even to minor changes of the water conditions. Unfortunately as we've all experienced, salinity reading equipment as...

www.bulkreefsupply.com

 

[JBendel]

Thank you! ... the Tropic Marine Hydrometer looks like my home brew hydrometer (about a ft long). I genenerally run under the rule, if I can't solve the problem 3 different ways and get the same answer, I am not there yet.

The irony is I spent the last year trying to figure out why the tank just wasn't as vibrant as in the past, and after all the rabbit holes, it's the salinity.

 

[this is me]

I use this to calibrate the refractometer once a year. Verify with RODI.

PINPOINT Salinity Calibration Fluid Inc.

PINPOINT Salinity Calibration Fluid is 53.0 mS standardized fluid for calibrating PINPOINT Salinity Monitors as well as refractometers. PINPOINT Salinity Calibration Fluid calibrates to sg 1.026 or 35ppt. PINPOINT Salinity Calibration Fluid calibrates to sg 1.026 or 35ppt. 2.2 FL OZ (65mL)...

www.bulkreefsupply.com

 

[danielm5]

I use this to calibrate the refractometer once a year. Verify with RODI.

PINPOINT Salinity Calibration Fluid Inc.

PINPOINT Salinity Calibration Fluid is 53.0 mS standardized fluid for calibrating PINPOINT Salinity Monitors as well as refractometers. PINPOINT Salinity Calibration Fluid calibrates to sg 1.026 or 35ppt. PINPOINT Salinity Calibration Fluid calibrates to sg 1.026 or 35ppt. 2.2 FL OZ (65mL)...

www.bulkreefsupply.com

I use something like this everyday I take a measurement!

 

[JohnK]

Calibration, slope, DIY standard, all by some guy named Randy;

https://reefkeeping.com/issues/2006-12/rhf/index.php

 

[dz6t]

The reason to calibrate a refractometer with 35 ppt calibration fluid (which is closer to the target salinity) is due to poorly manufactured inexpensive refractometers. The problem can be the precision of printing the scales and quality of the glass optics.

 

[JBendel]

Randy's article is about as "in depth" as it gets... that had to have taken a lot of time to put together,

"In fact, very few refractometers used by hobbyists are true seawater refractometers."

At least with a "35 ppt calibration solution", one shouldn't be too far off from actual salinity. but looking at my current +20yr old refractometer, might be time for an upgrade.