Salinity refractometer or meter, which to believe

Doug6952

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Hi,
I'm new to the forum, but not new to saltwater/reef. Been away from saltwater for about 15 years.
I have 2 refractometers, a Hanna salinity meter and an old school float hydrometer. Both refractometers have been calibrated with 1.026 solution and distilled water. The meter has been calibrated with the proper cal solution.
Both refractometers are showing the salinity @ 1.027. The meter is showing 1.024 and 1.025 at times. The hydrometer shows just a hair over 1.025.

Which would you believe is correct?

I'm thinking that the 2 refractometers are correct.
 
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Quietman

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They're all close...pick the one you're most comfy with and go with it. As long as you're checking calibration periodically which is key. Personally I like refractometers and don't see need to spend on anything digital. Plus I think wife is more impressed with holding that up to my eye than me just reading a number or pointer. :)
 
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Doug6952

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I bought a used tank and it came with a refractometer and the Hanna meter. I already had the other refractometer.
The meter is nice cause you dip it in and read it. Quick and easy. Plus it reads temp so 2 for 1. If it's not accurate the convenience takes a hit.
 
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dedragon

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I dont think the salinity meter is as consistent as refractometers, especially without calibrating before and after testing to make sure it hasnt lost calibration.
Float hydrometer (like tropic marin precision) or refractometers seem to be more consistent with results. This is just from reading on the forum though, i personally just use the refractometer.
 

arking_mark

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arking_mark

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Basically, I trust TM High-precision Hydrometer as the most reliable, because it's permanently calibrated. You just need to adjust for temp.

Using this, I was able to determine which of my easier meters to use.
 

MaxTremors

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Basically, I trust TM High-precision Hydrometer as the most reliable, because it's permanently calibrated. You just need to adjust for temp.

Using this, I was able to determine which of my easier meters to use.
‘Just need to adjust for temp’, which leads to the exact same problem. I have four different thermometers on my tank, which is regulated by an Inkbird, and the there is nearly 4° of difference between the four thermometers (2 cheap and 2 middle of the road), I assume the temp is somewhere in the middle, and use the one in the middle to match my water change water to, but that’s the issue with everything we use to test out tanks, none of it is pinpoint accurate. Which is why I always shoot for the middle of a range so if I’m too high or too low, hopefully I’m still within range.
 

arking_mark

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‘Just need to adjust for temp’, which leads to the exact same problem. I have four different thermometers on my tank, which is regulated by an Inkbird, and the there is nearly 4° of difference between the four thermometers (2 cheap and 2 middle of the road), I assume the temp is somewhere in the middle, and use the one in the middle to match my water change water to, but that’s the issue with everything we use to test out tanks, none of it is pinpoint accurate. Which is why I always shoot for the middle of a range so if I’m too high or too low, hopefully I’m still within range.

I have a calibrated thermometer that I use to calibrate my other thermometers. :)

 
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BoxKing

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Ive calibrated my Hanna once since Ive had it, and it hasn’t Budged out of calibration once.
Heres a little trick; if you have a digital scale, weigh Out the exact amount of salt it takes to get to the salinity you want when you mix… do this every time, and boom, not only will your salt mix dang near perfectly every time, you also mixed your very own calibration solution :) - do not worry about numbers like 34.9 vs 35ppt - check calibration if you don’t see equal to or greater than a .03 +/-

Digital testers are the only trusted method I use for all my testing - unless they’re unavailable, which I don’t bother doing either way bc I don’t test/dose MAG or trace elements.

Ps… I have three Hanna probes, and the Temp on all three vary.
 

Randy Holmes-Farley

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Heres a little trick; if you have a digital scale, weigh Out the exact amount of salt it takes to get to the salinity you want when you mix… do this every time, and boom, not only will your salt mix dang near perfectly every time, you also mixed your very own calibration solution :) - do not worry about numbers like 34.9 vs 35ppt - check calibration if you don’t see equal to or greater than a .03 +/-

How did you decide how much to add for this method?
 

dedragon

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How did you decide how much to add for this method?
Probably just a known volume of water and then weighed out the salt until they got to 35. They also said dont worry about 34.9 vs 35ppt, which i totally agree with, but i just use a known volume of salt (red solo cups of salt for me its 1 cup and a little extra). Im much worse at getting a consistent water level in my buckets needed to weigh out salt correctly
 

srobertb

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They're all close...pick the one you're most comfy with and go with it. As long as you're checking calibration periodically which is key. Personally I like refractometers and don't see need to spend on anything digital. Plus I think wife is more impressed with holding that up to my eye than me just reading a number or pointer. :)
Really? All my wife sees is her idiot husband spinning around squinting through a tube until accidentally I cross in front of my led fixture and crumble to the ground screaming “my eye!!! It burns!!! I’m baaahhhllliiinnndddd!!”
 
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srobertb

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How did you decide how much to add for this method?
I have a 50 gallon storage tank for saltwater hooked into an RODI. Sometimes I mix more at 10%, sometimes at 20%, sometimes I’ll top it off so there’s really know way to know exactly the water volume and so mixing by weight isn’t possible without a lot of work.

A red solo cup and practice and I typically get it around 1.020-1.030 then adjust from there. I aim for 1.0265. I figure if temps are the same and the new water and tank water both read the same I’m good (even if the digital refractometer isn’t perfect).
 

Randy Holmes-Farley

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I understand there are many ways to get to ones target salinity. I also understand that our aquaria are very forgiving of the exact salinity level.

But the "method" described by BoxKing seems problematic to me, and hence why I was asking how he decides how much salt to use. I don't understand how his measurement adds anything to the process.
 

BoxKing

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How did you decide how much to add for this method?
I do a 10% water change bi-weekly = 5gl. I mark the inside of the bucket with a water line; this ensures that I’m using two equal measures of RO/DI SALT/MIX each time, and not a “I’m close to the top where I usually fill my bucket method.” (Calibration method) - Then I use a digital scale (set to grams) and weighed out each scoop of salt in a container (RPM Pro) prior to adding to my RO/DI- typically 2.5 cups dials me in “close enough“. I target 35ppt, so I measured out each little addition required to achieve this number 1-2 times to test accuracy. 8/10 times I get 35ppt on the dot, the others were 34.9/35.2 - this is probably due to the fact that not every scoop will contain the exact equal measurements of elements. I make no corrections to salinity up or down if I’m within the range I like.

Now its a simple as setting the scale To grams, run a tare weight on the vessel I’m adding salt to, and fill to the desired weight.
 

BoxKing

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I understand there are many ways to get to ones target salinity. I also understand that our aquaria are very forgiving of the exact salinity level.

But the "method" described by BoxKing seems problematic to me, and hence why I was asking how he decides how much salt to use. I don't understand how his measurement adds anything to the process.
In theory I’m not really adding anything to the process, for me it subtracts. In the past I would continue to add/subtract a little here and there, wait for 20-30 and re-test, if not at the level I want, rinse and repeat if needed… hell it was tedious and added time to my routine.

I only check the final salinity now due to the ease of a conductivity probe/temp in one quick dip.
 

Randy Holmes-Farley

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I do a 10% water change bi-weekly = 5gl. I mark the inside of the bucket with a water line; this ensures that I’m using two equal measures of RO/DI SALT/MIX each time, and not a “I’m close to the top where I usually fill my bucket method.” (Calibration method) - Then I use a digital scale (set to grams) and weighed out each scoop of salt in a container (RPM Pro) prior to adding to my RO/DI- typically 2.5 cups dials me in “close enough“. I target 35ppt, so I measured out each little addition required to achieve this number 1-2 times to test accuracy. 8/10 times I get 35ppt on the dot, the others were 34.9/35.2 - this is probably due to the fact that not every scoop will contain the exact equal measurements of elements. I make no corrections to salinity up or down if I’m within the range I like.

Now its a simple as setting the scale To grams, run a tare weight on the vessel I’m adding salt to, and fill to the desired weight.

Sorry, I'm not following. If you are just adding salt and water to weight each time, why bother with the conductivity meter that is just "calibrated" to some unknown salinity that matches the 2.5 cups per gallon?

You do know that 35 ppt seawater cannot be made from 35 grams of salt mix plus 965 grams of RO/DI, right?
 
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