Refractometer Calibration Fluid Conundrum

blkhawk10 · Mar 4, 2026

I've had a bottle of one BRS sells for years now and didn't seem to have an issue. My buddy was suggesting I get a new bottle and see what the reading would be, so I did. The new calibration fluid is saying the old solution is off by .005 on the lower end so the salinity in my tank I just tested reads 1.030. Does the old solution dilute with age? I would think it would evaporate making the salinity in the old solution higher than the new solution. Everything in my tank other than an anemone seems to be doing ok. Should I go with the old or new calibration?

Gtinnel · Mar 4, 2026

If you have some basic kitchen scales its easy to make your own calibration solution from rodi water and table salt. You can also make it by measuring the volume of the salt instead of the weight.

There are instructions in this article

https://www.reefkeeping.com/issues/2004-06/rhf/

BryanM · Mar 4, 2026

This is why I went to a tropic marin hydrometer.

rtparty · Mar 4, 2026

Don’t trust any of the pre made calibration solutions. Make your own following Randy’s recipe and go off that

exnisstech · Mar 4, 2026

I used Randy's recipe and it works great. Recently I started using TM hydrometer and use it to measure my fresh mixed water. I then use that water to check the calibration on my refractometers but I don't use them very often now that I have the hydrometer. My tanks don't fluctuate enough that I feel the need to test them very often so the hydrometer is my go to tool. I'd like to try a conductivity meter but haven't talked myself into spending for one yet.

Randy Holmes-Farley · Mar 4, 2026

blkhawk10 said:
I've had a bottle of one BRS sells for years now and didn't seem to have an issue. My buddy was suggesting I get a new bottle and see what the reading would be, so I did. The new calibration fluid is saying the old solution is off by .005 on the lower end so the salinity in my tank I just tested reads 1.030. Does the old solution dilute with age? I would think it would evaporate making the salinity in the old solution higher than the new solution. Everything in my tank other than an anemone seems to be doing ok. Should I go with the old or new calibration?

It does not dilute with age unless you are in an environment of 100% humidity and leave it open all the time.

Commercial hobby standards have a shoddy reputation for accuracy. They are cheap and easy to make so why someone makes inaccurate ones is quite hard to understand.

I recommend making your own. This shows how. Be sure to use the refractometer recipe:

Reef Aquarium Salinity: DIY Calibration Standards

Reef Aquarium Salinity: DIY Calibration Standards By Randy Holmes-Farley One of the most important issues facing marine aquarists is providing a suitable environment for their aquaria's inhabitants. Among the important properties for a marine...

www.reef2reef.com

IceNein · Mar 4, 2026

I have always appreciated that the coke bottle method makes so much that it's nature minimizes measuring errors. And why not? Table salt and water are so cheap.