Trouble nailing salinity

Nano Gabe

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So Lately I’ve been having trouble while mixing my water nailing the salinity. I typically use my milwaukee refractometer and back up the reading with my hydrometer as a safeguard. And honestly my coralife hydrometer seems to always be spot on. I’m making water and I let it mix over night, in the morning I check with the Milwaukee and it tells me 1.027 which is weird because I know exactly how much salt I put in. Then I test with my hydrometer and it says 1.025. I grab my old manual refractometer which I never trusted to begin with and it tells me 1.024....... at this point I’m stumped so I recalibrate my Milwaukee and it now says 1.025 as well. Now I figure I’m okay adding that this water as the reading on the Milwaukee are matching my tank but I’m worried that the Milwaukee has been reading low the whole time and my tank and the water I just made are both really sitting at 1.024.... all the alk, calcium and mag are looking normal. What should I do?
 

SliceGolfer

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After calibrating the Milwaukee (at every use) there is a value you add or subtract from your reading for accuracy (At least I do). Zeroed out, mine reads +2 PPT higher than every other refractometer I have. The manual states the range of accuracy.
 
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Nano Gabe

Nano Gabe

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Man honestly this is such a headache and the reason I wanted a digital reading to begin with. With the hand held refractometer it always fluctuates I could test the water 3 different times and get different readings every time. Now I’ve been trusting the Milwaukee And I’m thinking it’s been reading a point higher then it really is the entire time. Which would make sense as my zoa’s have been half way closed the last few weeks.... the only thing I feel like that stays consistent is the coral life hydrometer which people say your not supposed to trust lol. I’m stumped I guess I can take a loss and just sell the Milwaukee I wasn’t aware of the +-.002 fluctuations and buy the Hanna salinity checker which I’ve heard is more accurate.
 

fermentedhiker

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That's my one gripe about the Milwaukee that you can't actually calibrate it, only zero it which is not the same. It should have a calibration function which allows you to zero it on RODI and then add a known sample of 1.026 and then calibrate to that. I've actually taken mine, zero it to RODI tested a sample of new(24hr old) salt mix. Test get a reading, retest same sample get a different reading, wait 5 minutes retest same sample get another reading(usually that one seems accurate). It seem like the sensor takes along time to normalize temperature with the sample or something.
 
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Nano Gabe

Nano Gabe

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That's my one gripe about the Milwaukee that you can't actually calibrate it, only zero it which is not the same. It should have a calibration function which allows you to zero it on RODI and then add a known sample of 1.026 and then calibrate to that. I've actually taken mine, zero it to RODI tested a sample of new(24hr old) salt mix. Test get a reading, retest same sample get a different reading, wait 5 minutes retest same sample get another reading(usually that one seems accurate). It seem like the sensor takes along time to normalize temperature with the sample or something.
For a device that’s over $100 I expect more accurate readings I’ve decided to sell it I can’t risk my tank being off
 
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Randy Holmes-Farley

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Your supposed to use Distilled water not RO/DI to zero the Milwaukee
That difference will be insignificant for a refractometer calibration, assuming it is 0-2 ppm tds and not 1300 ppm tds.
 

saltyhog

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My manual refractometer is very repeatable. If you put the same amount of water on the slide, use the same light and close the lid the same way each time (as well as wait 30 seconds if it's an automatic temp compensation unit) you should get repeatable readings.

All that said, I don't see how a difference of 0.001 in your water change is going to make a difference big enough to harm corals. The change in the DT salinity should be negligible.
 

fermentedhiker

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Thats the key word assuming the Distilled will be Zero Tds. Although I will probably regret arguing with a chemist.
Yeah no. TDS of distilled water has to be zero because it's distilled. I think Randy was using hyperbole to express if someone had a RODI unit in terrible shape so it had 1300tds.
For example my RODI unit has TDS of zero and measures 1.000 on the milwaukee, my RO stage with a TDS of 2 measures 1.000 and my tapwater with a TDS of 100-200 measures 1.000 on the Milwaukee. It's a case of a difference that makes no difference is no difference.
 
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Nano Gabe

Nano Gabe

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My manual refractometer is very repeatable. If you put the same amount of water on the slide, use the same light and close the lid the same way each time (as well as wait 30 seconds if it's an automatic temp compensation unit) you should get repeatable readings.

All that said, I don't see how a difference of 0.001 in your water change is going to make a difference big enough to harm corals. The change in the DT salinity should be negligible.
When I looked into it, the manual stated that the swing was +-.002 which I feel could be a huge difference. In my case I Always keep my tanks at 1.025 so +-.002 could be 1.023 or 1.027 the Hanna is +-.001 which I feel more comfortable with. Also it comes with calibration fluids which is great! Also it’s way more accurate in regards to temperature.
 

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