How accurate are refractometers?,

[Reef.]

Having issue keeping my salinity stable, it’s only out slightly, I’m guessing it’s a combination of misreading the refractometer, water changes and ato top offs.

if the blue line is on the 35ppt line, is there much of plus/minus margin? I’m thinking if there is a few of these margins will add up?

 

[Miller535]

They are accurate as long as you have calibration solution and are calibrating them. If not, they can be wildly inaccurate.

 

[Reef.]

They are accurate as long as you have calibration solution and are calibrating them. If not, they can be wildly inaccurate.

yeah I check calibration every use, it’s a d-d refractometer I believe it’s designed to be calibrated with rodi water, would it be useful to buy 35ppt calibration fluid?

 

[Miller535]

yeah I check calibration every use, it’s a d-d refractometer I believe it’s designed to be calibrated with rodi water, would it be useful to buy 35ppt calibration fluid?

Yes, while some say rodi water, it's best to calibrate with 35ppt solution because that is the range you are measuring. I am not familiar with DD. The other thing to make sure is that your refractometer is for marine/saltwater not a beer/brine refractometer.

 

[ahiggins]

They are accurate as long as you have calibration solution and are calibrating them. If not, they can be wildly inaccurate.

And the cal solution temp is the same as your tank water

 

[ahiggins]

yeah I check calibration every use, it’s a d-d refractometer I believe it’s designed to be calibrated with rodi water, would it be useful to buy 35ppt calibration fluid?

The only think I cal with rodi or plain water is my auto readers (digital). Any manual you want to cal with 35ppt

 

[X-37B]

Get a floating hydrometer. They are very accurate. I have the tropic marin one.
Great for cross reference.
I use my refrac 95% of the time.

 

[jda]

Most good ones will show true with both RO and calibration fluid... not all, so read up on what you need to do.

 

[vetteguy53081]

I use multiple units as I have been burned by false readings in the past

 

[redfishbluefish]

Also, don't forget to lubricate your refractometer....that threw me off until I figured it out.

Lubricate Your Refractometer

 

[Reef.]

Also, don't forget to lubricate your refractometer....that threw me off until I figured it out.

Lubricate Your Refractometer

would never have thought of that, thanks, good read too.

 

[ReefLab]

This is something that has been frustrating me with my reef lately

I have to calibrate before each reading, clean the lens and point it at a light just so to get a clear reading. Not to mention evaporation makes calibration fluid less reliable

 

[richarddeweerd]

Get a floating hydrometer. They are very accurate. I have the tropic marin one.
Great for cross reference.
I use my refrac 95% of the time.

I do the same. When I do a water change I check with the floating hydrometer an then I calibrate my refractometer to it. Between waterchanges I use the refractometer

 

[Heabel7]

YES use calibration fluid. I was using my RODI to calibrate and i was running 31ppt in tank when I figured it out. May have been cause of tank crash.
ALSO VERY IMPORTANT and rarely mentioned. Make sure you put the same amount of liquid on it. Too much or too little will give a different reading. Therefore if you have calibration fluid. You can put a set amount on let’s say 0.1ml. Set it to 35ppt. Then check it each time You make new water.

 

[chipmunkofdoom2]

They're accurate enough when used properly, but I didn't like the song and dance of rinsing, calibrating, testing, rinsing, testing again to make sure the first result was accurate, etc. I also don't like that they measure how light travels through a sample of water rather than the actual salinity of the water itself. If your water is a little cloudy or you want to know the salinity of a new batch of salt that hasn't settled yet, your readings could be completely off.

I moved to an American Marine Pinpoint Salinity monitor. This monitor and the KP Aquatics aquaculture rock I ordered were the two best ways I've spent money in this hobby yet.

 

[piranhaman00]

I recently purchased a veegee refractometer for improved accuracy, it has my head spinning. I have been in contact with support to get a better understanding maybe someone here can help.

The VeeGee Auto Temp Comp. (ATC) is set to 20C. Almost all (if not all) calibration fluids are standardized at 35ppt @25C. That means using a calibration fluid will inaccurately calibrate the Veegee. Make sense, so apparetnly you are supposed to use distilled or RODI water to calibrate this. At 20C pure water has a RI of 1.333 or sg of 1.000. This instrument is accurate enough to calibrate at 1.000 and be accurate across the board. Cheaper refracts cannot say this and that is why people say to use calibration fluid.

Ok so I have the VeeGee standardized at 20C, now when I read my aquarium water it is ATC to 20C so the reading is not the salinity at roughly 25C but at 20C. Is there a way to extrapolate to 25C? Is the difference that noticeable? The temperature variable for reading the refractive index of solutions is confusing me greatly.

Like @chipmunkofdoom2 posted above, I am tempted to switch to using a salinity montor like pinpoint that still relies on temperature but compensates. I do not like the idea of contaminating the probe when testing QT tanks which is where I test salinity the most. Ugh

Any thought on this?

 

[chipmunkofdoom2]

Like @chipmunkofdoom2 posted above, I am tempted to switch to using a salinity montor like pinpoint that still relies on temperature but compensates. I do not like the idea of contaminating the probe when testing QT tanks which is where I test salinity the most. Ugh

Any thought on this?

I don't often test the salinity of my QT system. It remains relatively stable. If I do, I usually do my normal cleaning routine, rinse the probe well with tap water and let it dry out for several days between uses. That should be enough to kill anything that may be in your QT tank.

If you want to be sure or you need to use it shortly after using in QT, you can disinfect with bleach. I contacted the manufacturer and they recommended a short dip in a 1:5 ratio of bleach to tap water to disinfect.

 

[piranhaman00]

I don't often test the salinity of my QT system. It remains relatively stable. If I do, I usually do my normal cleaning routine, rinse the probe well with tap water and let it dry out for several days between uses. That should be enough to kill anything that may be in your QT tank.

If you want to be sure or you need to use it shortly after using in QT, you can disinfect with bleach. I contacted the manufacturer and they recommended a short dip in a 1:5 ratio of bleach to tap water to disinfect.

Oh interesting.

I commonly get fish in around 1.015 and raise about 0.001 every few days through evap and concentrated salt water top off. I check the salinity daily!

Im really stuck between these two. How accurate have you found the pinpoint? How quickly does it temp stabilize?

 

[Albertan22]

I don't often test the salinity of my QT system. It remains relatively stable. If I do, I usually do my normal cleaning routine, rinse the probe well with tap water and let it dry out for several days between uses. That should be enough to kill anything that may be in your QT tank.

If you want to be sure or you need to use it shortly after using in QT, you can disinfect with bleach. I contacted the manufacturer and they recommended a short dip in a 1:5 ratio of bleach to tap water to disinfect.

Anyone running hyposalinity will be testing will be testing their QT tanks very frequently as you drop the salinity, work to hold it at the target, then ease it back up slowly. Accuracy is critical, but I also worry about cross contamination and like the fact that the refractometer never touches the tank.

 

[chipmunkofdoom2]

Anyone running hyposalinity will be testing will be testing their QT tanks very frequently as you drop the salinity, work to hold it at the target, then ease it back up slowly. Accuracy is critical, but I also worry about cross contamination and like the fact that the refractometer never touches the tank.

As I mentioned, if you need to test more frequently, you can disinfect the probe with a short dip in a 1:5 bleach:water solution. That will instantly kill anything that could potentially be on it.