Milwaukee refractometer reading off for standard solution
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fermentedhiker
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My digital is always off by .002 SG as well. I think the problem with the digital is you calibrate to RODI and not your actual target SG. Mine tests RODI correctly but 1.025 calibration solution always reads as 1.027. It would be interesting to see if I could get some 1.002 fluid and zero it to that if it would then read correctly for sea water levels.
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Phildago
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That's a great idea for an experiment. Mine is off by. 002 in the opposite direction so I can't help on that particular experiment. But if you have a milligram scale you can weigh out 9.974 g of rodi and mix in 26 mg of salt. This would give you a 10 ml 1.002 sg solution for calibration. It's worth a shot
Randy Holmes-Farley
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You can make a standard using table salt, such as per my articles. Assuming you can measure weights and volumes accurately, that will be much more precise than a hobby refractometer can measure.
You can’t make it with salt mix as you cannot know the amount of moisture in it, and also cannot just dry it. You also do not use exactly 35 grams per liter to get 35 ppt seawater equivalent using table salt.
You can’t make it with salt mix as you cannot know the amount of moisture in it, and also cannot just dry it. You also do not use exactly 35 grams per liter to get 35 ppt seawater equivalent using table salt.
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User1
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Thank you. Just came along the thread and oddly enough I also own a older milwaukee refractometer with similar drift or reporting. I used the old plastic hand held meters as a backup and/or reference along with Neptune's probe. I figure as long as they are all close I'm good - somehow I'm thinking that isn't the best approach...
I've been using Refractometer Claibration Solution by Aqua Craft Products which is a 35 ppt refractive index standard solution or so they say. I'll see if I can make your standard next week and see how it compares so wanted to say thank you for posting that.
fermentedhiker
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Thanks Randy. One thing that concerns me about the Milwaukee is that it accurately reads zero for RODI(the only "calibration" adjustment on the unit) but reads off at actual tank levels. Which makes me think the error is nonlinear and by zeroing it to 1.002 it still won't be accurate at a tank measurement. Of course trying it out and comparing it to a seawater standard will show this one way or the other I guess.
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Phildago
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Okay guys, so the results are in and the Milwaukee is actually spot on. I got another refractometer standard solution today for 35 ppt to use in the testing as well. I tested everything multiple times on the Milwaukee VS manual refractometer and it turns out the standard fluids are off. Measurements for all fluids and tank water were identical on the Milwaukee VS manual refractometer.
The calibration fluid measured 0 ppt and 1.000 sg on both refractometers.
My rodi water measured at 0 ppt and 1.000 sg on both refractometers.
The 1.025 sg standard solution measured at 1.023 sg on both refractometers.
The 35 ppt standard solution measured at 37 ppt on both refractometers.
My tank water measured 35 ppt on both refractometers.
Conclusion: Make your own standards.
The calibration fluid measured 0 ppt and 1.000 sg on both refractometers.
My rodi water measured at 0 ppt and 1.000 sg on both refractometers.
The 1.025 sg standard solution measured at 1.023 sg on both refractometers.
The 35 ppt standard solution measured at 37 ppt on both refractometers.
My tank water measured 35 ppt on both refractometers.
Conclusion: Make your own standards.
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Phildago
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Thank you again.
Yes the standard solutions seem to be off per my testing. I'm going to read your article on standard solutions and simply make my own because it's quite frustration that they seem to be off.
Ive done a few years of formal laboratory work (patch clamp electrophysiology), so I have a good grasp on the basics for making solutions, but I also want to make sure I'm not overlooking anything.
I'll make a good standard and report back on my results.
Randy Holmes-Farley
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Glad this is resolved. 
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Phildago
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What's your favorite was to desiccate at home? Would the microwave be sufficient or do items need to be baked to properly do the job?Glad this is resolved.
Randy Holmes-Farley
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if you are talking about table salt, use a regular oven. Don’t even try with salt mix.
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Phildago
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Yup regular table salt. Thanks, I'm going to give that a shot. My balance is accurate enough to make the reference solution by weight, so I'm going to try to be as precise as possible
Acros
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I got a new MA887 and have the same issue with the standard 35ppt solution reading 37ppt.
Do you still stand by the finding from this experiment? I am just wondering if any of your opinions/results on this have changed.
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Phildago
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I haven’t retested again. I have been using my Milwaukee to set my rank salinity and everything has been great though.
