Milwaukee refractometer reading off for standard solution

Phildago · Dec 28, 2019

I just received a brand new Milwaukee refractometer and the reading for the standard solution is off. The standard is 1.025, but reading is coming in at 1.023 no matter how many times repeat and/or recalibrate.

I haven't tested my tank water yet because I don't know what to do with this

information. Could the solution be off? That doesn't seem right.

Maybe the next step will be to test with a manual refractometer and see is its 1.023 or 1.025 and compare to the Milwaukee.

If the instrument is coming in at .002 off consistently would this be grounds to return the unit? Can it be recalibrated to read correctly from home? And since it's consistent.. How would this translate into tank readings? Would they also be off by .002 or would it translate differently at another salinity?

Sorry for all the questions, but this is my first time using the unit and I'm just trying to get an idea of how to interpret this

Randy Holmes-Farley · Dec 28, 2019

What solution?

Phildago · Dec 28, 2019

Randy Holmes-Farley said:
What solution?

The naslow chemicals Ltd 1.025 sg standard solution

Randy Holmes-Farley · Dec 28, 2019

Do you have a link to it? I can’t find any info.
Does it claim to be a seawater standard? A simple specific gravity standard is not suitable for this purpose.

Randy Holmes-Farley · Dec 28, 2019

Most of what I see is the same discussion by me a few years ago here,

NHgoalstop · Dec 28, 2019

How much solution are you putting in? When I use mine, I put in just enough to cover the mirror. Sometimes if I put in too much I get a bad reading.

Be102 · Dec 28, 2019

I actually had the same thing.. got mine today and first calibrated w Rodi and said 1.024 then tried with the solution and also said similar .. I then tried to calibrate and test my .35 ppt solution and it came to I think .34 and I gave up and said close enough

SeaDweller · Dec 28, 2019

Mine was spot on when I used it a few times in the beginning. Try warming up the metal plate around the sensor and see if it helps.

Randy Holmes-Farley · Dec 28, 2019

I would not be certain that is suitable for a refractometer without knowing more about it.

Phildago · Dec 28, 2019

Randy Holmes-Farley said:
Do you have a link to it? I can’t find any info.
Does it claim to be a seawater standard? A simple specific gravity standard is not suitable for this purpose.

It just says 1.025 seawater calibration validation solution. Another user posted a picture above

NHgoalstop said:
How much solution are you putting in? When I use mine, I put in just enough to cover the mirror. Sometimes if I put in too much I get a bad reading.

I tried different amounts between filling the chamber and just covering the mirror. It's spot on 1.023 every time.

SeaDweller said:
Mine was spot on when I used it a few times in the beginning. Try warming up the metal plate around the sensor and see if it helps.

It was at room temp. 72 degrees

NHgoalstop · Dec 28, 2019

Randy Holmes-Farley said:
I would not be certain that is suitable for a refractometer without knowing more about it.

Is he using the same one I bought (MA887) it's labeled as a saltwater refractometer.

Phildago · Dec 28, 2019

Randy Holmes-Farley said:
I would not be certain that is suitable for a refractometer without knowing more about it.

Its the one that comes in the box with the unit. I don't know much about it, but it's what the company selected as a standard

Be102 · Dec 28, 2019

I also don’t see there being a problem with it: however I tried Rodi as well and I still got an error. Maybe we got some that are off a little?

Phildago · Dec 28, 2019

Be102 said:
I also don’t see there being a problem with it: however I tried Rodi as well and I still got an error. Maybe we got some that are off a little?

When I get home I'm going to toss some of that solution in my manual refractometer and see what I get... That'll help us know if the solution is off or if the units are.

From there, provided the solution is good, I'd like to figure out if the unit is off by .002 with tank water as well.

If the unit is consistently off by .002 every time I use it then I'd probably be okay with that and just manually adjust the values on the back end. What I'm most worried about is if the skew changes with varying salinities

dragon99 · Dec 28, 2019

My Milwaukee digital refrac has the same issue. I've just come to accept that 37ppt is actually 35. It reads 2ppt low with any calibration solution I've tried (brightwell, brs, and included). I've checked it against a standard refractometer and my apex probe and it's consistently 2ppt low.

Phildago · Dec 28, 2019

dragon99 said:
My Milwaukee digital refrac has the same issue. I've just come to accept that 37ppt is actually 35. It reads 2ppt low with any calibration solution I've tried (brightwell, brs, and included). I've checked it against a standard refractometer and my apex probe and it's consistently 2ppt low.

Thanks good to know.

X-37B · Dec 28, 2019

I had the same issue and sent it back. I use a BRS unit now.

Randy Holmes-Farley · Dec 28, 2019

NHgoalstop said:
Is he using the same one I bought (MA887) it's labeled as a saltwater refractometer.

I’m referring to the solution, not the refractometer.

Randy Holmes-Farley · Dec 28, 2019

Phildago said:
Its the one that comes in the box with the unit. I don't know much about it, but it's what the company selected as a standard

well, hopefully they selected it properly. My 35 ppt standard solutions for hydrometers or conductivity meters are not suitable for a refractometer.

Phildago · Dec 28, 2019

Randy Holmes-Farley said:
well, hopefully they selected it properly. My 35 ppt standard solutions for hydrometers or conductivity meters are not suitable for a refractometer.

Ah, okay. Thank you Dr. Farley.

I have another question that Im not sure how else to go about finding the answer to. If I were to make an at home solution at 35 ppt, would I be able to use instant ocean reef salt, or should I use table salt?
The reason I ask is because I would make this solution based off weight of solute/solvent, and I'm not sure how ion balance measures into the equation of light refraction. For example if instant ocean contains 3% some mineral that doesn't change the refraction it might be unsuitable compared to pure NaCl. I also may be over thinking this but I'd like to be as precise as possible