Refractometer issues

raythereefer · Aug 11, 2024

When testing My salinity the first reading will usually be high , followed by the reading dropping slightly every time . Has anyone else had this issue or is my refractometer ready for the bin ? Have calibrated it to 0 using R.O but it always does this. First test can be as high as 1.032 and generally gets to the stage where it will settle between 1.025 - 1.027 for half a dozen tests in a row but just makes me uneasy that I'm getting different readings. But always starting high and gets gradually lower ?

crazyfishmom · Aug 11, 2024

raythereefer said:
When testing My salinity the first reading will usually be high , followed by the reading dropping slightly every time . Has anyone else had this issue or is my refractometer ready for the bin ? Have calibrated it to 0 using R.O but it always does this. First test can be as high as 1.032 and generally gets to the stage where it will settle between 1.025 - 1.027 for half a dozen tests in a row but just makes me uneasy that I'm getting different readings. But always starting high and gets gradually lower ?

Calibrating with RODI may not be the best way to go. As far as I understand, it is recommended that you purchase a calibration solution at 35 ppt and use that instead of RODI.

raythereefer · Aug 11, 2024

crazyfishmom said:
Calibrating with RODI may not be the best way to go. As far as I understand, it is recommended that you purchase a calibration solution at 35 ppt and use that instead of RODI.

I understand that but even still it doesn't explain why my test results are slowly dropping from 1 minute to the next ?

Randy Holmes-Farley · Aug 11, 2024

raythereefer said:
When testing My salinity the first reading will usually be high , followed by the reading dropping slightly every time . Has anyone else had this issue or is my refractometer ready for the bin ? Have calibrated it to 0 using R.O but it always does this. First test can be as high as 1.032 and generally gets to the stage where it will settle between 1.025 - 1.027 for half a dozen tests in a row but just makes me uneasy that I'm getting different readings. But always starting high and gets gradually lower ?

What refractometer?

Sounds like it may be a temperature equilibration issue. I’d suggest taking a water sample, let it sit next to the refractometer for a while (an hour maybe) then try it and see if the same thing happens.

redfishbluefish · Aug 11, 2024

Agree with using a calibration solution....but that doesn't address the drifting numbers.

How old is the refractometer? And does the little swinging cover plate swing freely?

Might wish to check out this post:

Lubricate Your Refractometer

raythereefer · Aug 11, 2024

Randy Holmes-Farley said:
What refractometer?

Sounds like it may be a temperature equilibration issue. I’d suggest taking a water sample, let it sit next to the refractometer for a while (an hour maybe) then try it and see if the same thing happens.

Quite an old one judging by the box ! Will give that a go thanks randy I suppose temperature equilibration could make sense as the more tests I do i suppose the closer the temperature matches and generally more settled the results become. Maybe time to grab a new one to be sure regardless

raythereefer · Aug 11, 2024

redfishbluefish said:
Agree with using a calibration solution....but that doesn't address the drifting numbers.

How old is the refractometer? And does the little swinging cover plate swing freely?

Might wish to check out this post:

Lubricate Your Refractometer

Probably older than me by the looks of it that is swinging fine so that's one more thing to rule out but thanks for the insight