Which to believe...Milwaukee Refractometer or Tropic Marin High Precision Hydrometer?

JasonG1 · May 25, 2023

Hi all. Wondering what you'd do...

My new Tropic Marin High Precision Hydrometer is reading my tank at 1.0235 SG while my Milwaukee Refractometer is reading 1.022. What gives? The Milwaukee was calibrated as instructed with RODI water (direct from my new BRS 5 Stage Premium Plus 150 GPD Water Saver RO/DI System). I've heard the Hydrometer is the ultimate in precision, but it's recommended to get the milwaukee for convenience (and accuracy). What would you do in this situation? Thanks!

piranhaman00 · May 25, 2023

The milwaukees are not very accurate, however at 1.035 you would see some negative effects I would think

Nburg's Reef · May 25, 2023

Get some 35ppt (or 1.026 ash) solution and check. I’d trust which one reads the saltwater reference over a zero cal like distilled water.

delv2323 · May 25, 2023

I would trust the hydrometer all things being equal. Perhaps make a reference solution and compare, that's an enormous difference and I would want to be 100% certain.

I have had refractometers vary so wildly month to month and even multiple new unused reference solutions disagreeing by meaningful amounts.

Why not confirm the hydrometer then calibrate an easy to read swing arm hydrometer that you keep clean and re-calibrate occasionally? A swing arm hydrometer is the quickest to use and easiest to read...doesn't require electricity or full sun. Both will last forever.

JasonG1 · May 25, 2023

I'm so sorry...I originally incorrectly stated the Hydrometer was 1.035 above when it IS ACTUALLY 1.0235. And the Refractometer is 1.022. Still...quite different. I corrected my original post above to say 1.0235. It sounds like the Milwaukee, while convenient, is not as accurate as I was hoping (for the cost). It sounds like I should trust my hydrometer most.

Bozburn · May 25, 2023

I picked up a Hydrometer and use that to help confirm my refractometer I use.

I was using a hannah salinity checker but that thing is crap. Would calibrate it every week and it would still be way off, so I got the refractometer and hydrometer and use those together.

EeyoreIsMySpiritAnimal · May 25, 2023

JasonG1 said:
I'm so sorry...I incorrectly stated the Hydrometer was 1.035 when it IS ACTUALLY 1.0235. And the Refractometer is 1.022. Still...quite different.

1.What's the margin of error for the Milwaukee?
2. What is the water temp (and did you calculate/adjust the Tropic Marin result based on this)?

mckinney0171 · May 25, 2023

You need to get a Vee Gee refractometer - calibrate it to a known salinity. And you will never second guess a reading again.

EeyoreIsMySpiritAnimal · May 25, 2023

mckinney0171 said:
You need to get a Vee Gee refractometer - calibrate it to a known salinity. And you will never second guess a reading again.

Ideally, you would calibrate your refractometer (with a solution of known salinity) before each use and adjust accordingly... No second guessing needed.

Edit: I do this when using a handheld refractometer for quick adjustments when mixing saltwater... and yes, I do a calibration read EACH TIME I test during that mixing session. No reason to skip that step when it takes 3 seconds.
Final check with the Tropic Marin (I'm afraid of breaking it so try to handle it sparingly, lol)

Tcook · May 25, 2023

The Milwaukee margin of error can be a full point. Mine can vary like that. My TM hydrometer was a bit off. Make some of Randy’s test solution and calibrate you TM.

JasonG1 · May 25, 2023

Thank you for mentioning adjusting the Hydrometer for temp...I completely forgot that step and here are my new results which are less concerning, but still interesting:
Hydrometer: 1.023 (adjusted for temp)
Refractometer: 1.022 (calibrated using RODI)

Refractometer accuracy is supposed to be +/- 0.002 SG

So 1.023 versus 1.022...actually not too bad! Wow...this exercise with you all has actually taught me a lot (especially to get more familiar with my hydrometer scale and adjust for temp (I found and used this: https://www.morebeer.com/content/hydrometer_correction_calculator)...and that my Refractometer is not terribly accurate and maybe I won't use much except for quick convenient checks.

I'll check out the Randy's test solution suggestion. Thank you!

Randy Holmes-Farley · May 25, 2023

Within the accuracy of each, they may both be perfectly accurate.

The milwaukee, for example, only claims 1.0235 means 1.0215 to 1.0255

Milwaukee MA887 Digital Salinity Refractometer

The Milwaukee Instruments digital salinity refractometer is ideal for saltwater aquarium professionals and enthusiasts.

milwaukeeinstruments.com

ACCURACY: ±2 PSU | ±2 ppt | ±0.002 S.G. (20/20) | ±0.3°C / ±0.5°F

piranhaman00 · May 25, 2023

I use a Veegee as well, the only true refractometer on the market, calibrate with RODI to 0.000 and will be accurate at any level. Other refractometers ATC to 25C even though reference solution are set to 20C.
I also use Hanna and find it works amazing, not sure about all the negative reviews I hear, I’ve only calibrated it once in 2 years now and it’s dead on with Veegee

JasonG1 · May 25, 2023

piranhaman00 said:
I use a Veegee as well, the only true refractometer on the market, calibrate with RODI to 0.000 and will be accurate at any level. Other refractometers ATC to 25C even though reference solution are set to 20C.
I also use Hanna and find it works amazing, not sure about all the negative reviews I hear, I’ve only calibrated it once in 2 years now and it’s dead on with Veegee

Which Hanna Salinity tester do you have? I see they have several options.

EeyoreIsMySpiritAnimal · May 25, 2023

@Randy Holmes-Farley , is a conductivity probe more accurate than the other options we've been discussing? Does this also need frequently calibration?

areefer01 · May 25, 2023

piranhaman00 said:
I use a Veegee as well, the only true refractometer on the market, calibrate with RODI to 0.000 and will be accurate at any level. Other refractometers ATC to 25C even though reference solution are set to 20C.
I also use Hanna and find it works amazing, not sure about all the negative reviews I hear, I’ve only calibrated it once in 2 years now and it’s dead on with Veegee

Glad it is working although Hanna recommends monthly.

Randy Holmes-Farley · May 25, 2023

EeyoreIsMySpiritAnimal said:
@Randy Holmes-Farley , is a conductivity probe more accurate than the other options we've been discussing? Does this also need frequently calibration?

Some are, some aren't. The best conductivity probes, calibrated properly, will be more accurate than most other devices.

That said, making cheap anything doesn't always lend itself to accuracy.

I am a fan of higher end, 4 electrode conductivity meters/probes, even if they are purchased used from a place such as ebay.

I have an old Orion model 128 with a 4 electrode probe that worked perfectly for many years (still does, I think). It actually cannot be calibrated, but it can be checked in a standard, and corrected as needed. It never varied from reading a bit low in a commercial KCl standard over many years. I don't recommend leaving them in reef tank water 24/7 to reduce fouling.

RichReef · May 25, 2023

My TM Hydrometer crashed my tank. 1.035.

Salty_Northerner · May 25, 2023

piranhaman00 said:
I use a Veegee as well, the only true refractometer on the market, calibrate with RODI to 0.000 and will be accurate at any level. Other refractometers ATC to 25C even though reference solution are set to 20C.
I also use Hanna and find it works amazing, not sure about all the negative reviews I hear, I’ve only calibrated it once in 2 years now and it’s dead on with Veegee

I agree with you about the Hanna tester. I was so surprised that my refractometer was off even after calibration. I'd zero it and test. The SG was reading 1.025 bang on and the Hanna was reading 1.021 after calibration. So down to my lfs and checked the refractometer against his many hundred dollar one and then tested it against the new IO swing arm and the 20+ year old IO swing arm, and believe it or not but the swing arms being totally a different shape tester were both identical and pretty much eyeballing it was so close to his refractometer.

So in the trash the refractometer went as it was the problem to the issue.

Hanna tester is reading 1.025 and comparing both swing arms and LFS refractometer the water is reading the test equipment to 1.0255 so I can live with that and it's in the margin of % Hanna claims so I'm happy with that and not concerned of a .001 +/- as everything we use isn't 100% accurate