Milwaukee Digital Refractometer

ataller

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My digital refractometer appears to be out of calibration. Using RODI I will zero the unit and then test my sample.

When I test known calibration solutions at 35 ppt, they always read 37ppt.
I have two different calibration solutions and they both report 37ppt.

I have been running my tank at 37ppt as per the refractometer assuming that it is actually 35ppt.

Does this sound reasonable? Should I buy another method of testing salinity ?
Should I trash this Milwaukee ? It is around 4 years old.
 
AS

arking_mark

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My digital refractometer appears to be out of calibration. Using RODI I will zero the unit and then test my sample.

When I test known calibration solutions at 35 ppt, they always read 37ppt.
I have two different calibration solutions and they both report 37ppt.

I have been running my tank at 37ppt as per the refractometer assuming that it is actually 35ppt.

Does this sound reasonable? Should I buy another method of testing salinity ?
Should I trash this Milwaukee ? It is around 4 years old.

I was always under the impression that one needs to calibrate these things at or near 35ppt.
 

arking_mark

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Looks like you are right. Might be time for a new meter. However, the one thing I will note is that salinity measurements by different meters are never the same.

I have 3 relatively new meters less than a year old and after calibration with their reference fluids get different readings:
Hanna: 35.6ppt
GHL: 34.4ppt
Other probe: 37ppt

They are probably all "right" using their measument methodologies.

I'm using my GHL as my "right" salinity. In the end, stability is probably what's more important.
 
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ataller

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Looks like you are right. Might be time for a new meter. However, the one thing I will note is that salinity measurements by different meters are never the same.

I have 3 relatively new meters less than a year old and after calibration with their reference fluids get different readings:
Hanna: 35.6ppt
GHL: 34.4ppt
Other probe: 37ppt

They are probably all "right" using their measument methodologies.

I'm using my GHL as my "right" salinity. In the end, stability is probably what's more important.
Probably best if I pick up a secondary to reference.

For now I’ll leave everything at “37” which based on the reference solutions should actually be 35.
 
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My digital refractometer appears to be out of calibration. Using RODI I will zero the unit and then test my sample.

When I test known calibration solutions at 35 ppt, they always read 37ppt.
I have two different calibration solutions and they both report 37ppt.

I have been running my tank at 37ppt as per the refractometer assuming that it is actually 35ppt.

Does this sound reasonable? Should I buy another method of testing salinity ?
Should I trash this Milwaukee ? It is around 4 years old.

Because it's calibrated by zeroing out with RODI they're always about .2 ppt off.

Should have been made to calibrate using a .35 solution.

The ones I know mix to about .33ppt with that meter.
 

Waters

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I have found two things with that meter that now allows me to get consistent, accurate readings. One is to make sure you completely fill the lens with the sample water....almost completely covering the silver area. The second is to let the sample sit for a minimum of a minute before reading.
 

BostonReefer300

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Looks like you are right. Might be time for a new meter. However, the one thing I will note is that salinity measurements by different meters are never the same.

I have 3 relatively new meters less than a year old and after calibration with their reference fluids get different readings:
Hanna: 35.6ppt
GHL: 34.4ppt
Other probe: 37ppt

They are probably all "right" using their measument methodologies.

I'm using my GHL as my "right" salinity. In the end, stability is probably what's more important.
+1 on stability is what matters when you're generally in the acceptable range. That being said, I also get different readings when I use my calibration standard solution on my Milwaukee MA887, my Apex salinity probe (which is finally appropriately calibrated---what a pain), and my old manual refractometer even when all are testing room-temperature equilibrated sample. I've given up stressing about it as long as the readings aren't that far off of each other. I aim for an average of 1.025 SG / 33.5 ppt between Milwaukee and Apex under the theory that if I'm actually at 1.024 - 1.026, then I'm fine.
 

BostonReefer300

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Not sure which video your watching, but they suggest to use distilled water, not RO/DI. It does make a difference.
They do say this but Dr. Holmes-Farley debunked this exact point a couple weeks ago on another thread. If I can find it, I'll post a link
 
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