Refractometer help how do you calibrate?

[joekool]

I have a BRS refractometer and BRS says to use there solution and I have for a few years to calibrate. It is the ATC unit.

They say don't use RO water and to use the solution that comes with it because that was made for it.

Some people do but if I do that it drops 0.05

I keep my tank at 35 ppt or 1.0265


What are you using to calibrate?

 

[joekool]

I also find it hard to believe that my LFS would keep there water at 1.018 or 1.020 which is the water that came home with my new fish today.

I need to get the Red Sea refractometer it is made for marine water not brine water

 

[Randy Holmes-Farley Verified Community Expert]

Use the 35 ppt seawater standard for proper calibration. That can never be wrong (assuming it was made properly and the device physically allows you to use 35 ppt/sg = 1.0264)).

Calibration using RO water only works perfectly if it is a true seawater refractometer and not a brine refractometer (most are the latter).

Lots of LFS use low salinity for fish, possibly because they thing it helps with disease, and possibly because they don't want to spend more on salt mix.

 

[mike007]

Are you saying with the Redsea refractor we need to calibrate with ro water? Also do we need to match the temp of ro water with the tank sample? I tried Pinpoint salinity solution but the results were far apart when I calibrated with ro.

 

[joekool]

I had a difference of .05 with RO under what the solution calibrates too.

My LFS is using the same one as I have. I'm sure of it. They use RO. I asked them why there's was lower than norm
believe it or not my hydrometer has been very close to my refractometer even though I don't use that thing.

Mine calibrates and stays there but I do keep checking.

Was odd that the water in my bag was 0.018 wow took awhile to aclimate my fish to .0265

 

[Randy Holmes-Farley Verified Community Expert]

Are you saying with the Redsea refractor we need to calibrate with ro water? Also do we need to match the temp of ro water with the tank sample? I tried Pinpoint salinity solution but the results were far apart when I calibrated with ro.

No. I'm saying it is never wrong to use a 35 ppt standard. For the Red Sea real seawater refractometer, fresh water should also work (assuming that is the one we are talking about, and assuming it really is a true seawater refractometer).

The closer the temps are (especially the room/refractometer temps during calibration and measurement, the less need there is to rely on the ATC function of the device, which may not be perfect.

 

[Randy Holmes-Farley Verified Community Expert]

I had a difference of .05 with RO under what the solution calibrates too.

My LFS is using the same one as I have. I'm sure of it. They use RO. I asked them why there's was lower than norm
believe it or not my hydrometer has been very close to my refractometer even though I don't use that thing.

Mine calibrates and stays there but I do keep checking.

Was odd that the water in my bag was 0.018 wow took awhile to aclimate my fish to .0265

When you say, "difference of .05", what does that mean? It can't be literally true, I don't think.

1.02 vs 1.07?
1.020 vs 1.025?
1.0200 vs 1.0205?

 

[StikHedRon]

How can I tell which refractometer I have? I got the one from Dr Foster and Smith - $39.99 one

 

[joekool]

It is a difference of .005 is what I meant. And yes if I use RO that is the difference vs the calibration fluid.

The LFS is using the same refractometer I am and they have been calibrating it with RO.

I had to aclimate my new fish from 1.018 to 1.0265

I think they are confused about there unit. I have called them out before on there water.

 

[joekool]

How can I tell which refractometer I have? I got the one from Dr Foster and Smith - $39.99 one

This unit is a brine unit and requires calibration fluid to calibrate correctly.

 

[TJ's Reef]

I have a Milwaukee Refractometer and just use RO/DI for calibration. When compared to the calibration fluids was nearly spot on. Our water here is nearly usable out of the tap though rarely exceeding 18 ppm TDS and almost no heavy metals present. All this mountain rain out here has its advantages... lol

Cheers, Todd

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, brine refractometers should be off by only a small amount (if perfectly made) when reporting in units of specific gravity (a real 1.0264 reads as 1.0261, or 0.003 too low).

The error is seemingly much larger if read in ppt units, where 35 ppt reads as 36.7 ppt.

BUT, any device is best calibrated near to the values you are interested in measuring. In fact, if you target 35 ppt and use 35 ppt for calibration, it hardly matters if the device is accurate at all, since that point will match. This is the real world, and cheap devices may not have the accuracy of scientific instruments, so calibrating with seawater seems prudent to me, even if it is a seawater refractometer (unless you have at least once verified that calibration with RO/DI gives the same results.

 

[specvjeff]

I've always just used rodi water to calibrate. Done the job for many years. There are solutions that are said to be more accurate but I've never felt the need to use them.

 

[Randy Holmes-Farley Verified Community Expert]

I've always just used rodi water to calibrate. Done the job for many years. There are solutions that are said to be more accurate but I've never felt the need to use them.

It has done the job because organisms are, fortunately for us, not very sensitive to the exact salinity.