Jestersix

Salinity

Vhuang168 said:
Brine or Salt solution is =/= Sea Water. Lots of other 'salts' make up what is in seawater. Refraction will be different because of that. That is why refractometers scaled for brine are not recommended for aquarium use.
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Of course a NaCl solution doesn't equal seawater. I was just using a method that the manual for the Milwaukee Digital Seawater Refractometer MA887 to confirm that the refractor was correctly calibrated using RODI water.
 
So if I measure a 35ppt water after heating it to 90 degree using a perfectly calibrated refractometer. You think it will read 35ppt?
rygh said:
Disagree.
Sure, the refraction index is certainly sensitive to temperature.
But refractometers have a bimetallic strip inside attached to the optics that compensates for temperature.
Plus, unless you store the instrument outside in the sun/snow, it really does not change all that much.

Key though: That bimetallic adjustment is not instant. It needs some time to adjust.
So you need to keep the instrument (not the water) stored in the same place you measure it,
plus you need to give it a few seconds for that little drop of water to adjust to temp of instrument.
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Did you read the material I included? The pdf is about lab grade salinity measurments equipment which has circuits for temp compensation yet they will say you better do the measurment in 25c.
 
I have a question: if we mix a 35ppt at 77 degree temp. Then we heat the water to 90 degree.
Would we expect the salinity of the water to be other thsn 35ppt?

What is the ppt value if we use a refracto that was calibrated at 77degree Would it show 35ppt?

What is the ppt if we measure using a refracto that is calibrated at 90 degree condition? Would it read 35ppt?

My understanding is that even when we do salt mix the ppt is spec'ed at certain temp range. So mixing cold water..
Say 50degree. and measuring 35ppt, will yield difftent ppt when wate us heated up to room temp of 78degree.

I know this because my mixing station and my refracto, my pinpoint prob all in the garage and dying winter the room temp is very cold whole during summer I deal with 85 to 90 degree temp. That's why I had to pay attention to the temp of the salt mix and the refracto temp range when I do salinity measurments..
 
ofzakaria said:
I have a question: if we mix a 35ppt at 77 degree temp. Then we heat the water to 90 degree.
Would we expect the salinity of the water to be other thsn 35ppt?

What is the ppt value if we use a refracto that was calibrated at 77degree Would it show 35ppt?

What is the ppt if we measure using a refracto that is calibrated at 90 degree condition? Would it read 35ppt?

My understanding is that even when we do salt mix the ppt is spec'ed at certain temp range. So mixing cold water..
Say 50degree. and measuring 35ppt, will yield difftent ppt when wate us heated up to room temp of 78degree.

I know this because my mixing station and my refracto, my pinpoint prob all in the garage and dying winter the room temp is very cold whole during summer I deal with 85 to 90 degree temp. That's why I had to pay attention to the temp of the salt mix and the refracto temp range when I do salinity measurments..
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As I understand it,

No

No

Yes

Correct


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ofzakaria said:
So when we mix we need to mix at the target temp that is specified on the salt mix for correct ppt, or the system target temp which usually is the range the salt mix vendor spec for..
Is this statment correct?
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This is why I weigh my salt and add to a specific amount of water.


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Vhuang168 said:
As I understand it,

No

No

Yes

Correct


Sent from my iPad using Tapatalk Pro
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That was also my understanding, we should consider temp when we mix salt.
And We should consider temp when we calibrate.

The final piece of the puzzle is the refracto temp range. This is a nice paper from UC talk in details about the hand held refracto.
It describe how these common refractos can compensate only withen specific range and outside this range the refracto will yield less accuracy

Quotes from the paper:

"Newer refractometers compensate for fluctuations in temperature, but are still only accurate within a specified range of temperatures."

"2. Note the temperature at the time of readings. Most ATC refractometers operate properly in the 68-86ºF range. A laboratory or office at room temperature should be used if outside temperatures exceed the manufacturer's recommended temperature range."

That is why it is important to understand the capabilities and spec of the tool we use to measure salinity if we seek accurate measurments.
It's also important to know of the refracto we use have ATC or not and at what range its ATC is valid

Finally, this is direct qoute from redsea refracto manual, this refracto is calibrated and to be used at 77 degree

"Automatic temperature compensation (ATC) compensates for a few degrees of difference between the ambient temperature and the calibrated temperature of the refractometer. Larger temperature variations will give an error of approximately 1.0ppt in the salinity reading.

ATC does not adjust the PPT reading of a refractometer to the temperature of the aquarium!"


Thank you Vince and Mike
 

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Sorry for the posts btw. Salinity is something am strict with cause salt mix is where all start when it come to paramaters and keeping solid levels
 
Coral reefer said:
I mix cold, around 60 degrees.
I add salt by volume, to volume of water then check SG after it has mixed.
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For sure weighing is good approach, but I think having accurate salinity measurment is still crucial cause I have seen many times where the salt from the top of the bucket mix differently than the bottom of the bucket. I read somewhere this is common because salt settle or something around these lines. Which means the ammount of salt needed for a 35ppt a gallon os diffrent at some diffrent levels from the bucket. I have seen this many times and it used to confuse the hell out of me..

Many times I help someone steuggling with elevated paramater level that end up being due to a faulty salinity measurments.
 
ofzakaria said:
For sure weighing is good approach, but I think having accurate salinity measurment is still crucial cause I have seen many times where the salt from the top of the bucket mix differently than the bottom of the bucket. I read somewhere this is common because salt settle or something around these lines. Which means the ammount of salt needed for a 35ppt a gallon os diffrent at some diffrent levels from the bucket. I have seen this many times and it used to confuse the hell out of me..

Many times I help someone steuggling with elevated paramater level that end up being due to a faulty salinity measurments.
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It’s usually not salt but the additives for Alk/Ca that settle out.

But in my case, I don’t do water changes so that is 1 issue I don’t have to deal with.


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Omar- I’m not totally sure where you were going with your several questions/thought experiments. The bottom line is that if you’ve calibrated your refractometer at a certain temperature, then you should use it near that temperature. So since I think the norm would be to have it calibrated at room temperature, if you store your water someplace cold or hot, you bring out of the tank or storage area into the room-temperature room and measure at that temp.

Automatic temperature correction on refractometers is very helpful, it will make it so that you don’t need to worry about your exact temperature as long as you are not calibrating vs testing in markedly different temperatures.

Regarding temp and salinity measurement (reinforcing what was already said)- Colder water fundamentally has a higher refractive index (reads higher salinity on a refractomer) without actually having a higher salinity. Not to be confused with the issue of how much salt can dissolve into water of different temperatures, which is a totally different issue but is easy to confuse. There is a negligible change to actual salinity at different (reasonable) temps. So if you make up water to 35 ppt at room temp, it will still be 35 ppt when you add it to your tank and it warms up.
 
JVU said:
Omar- I’m not totally sure where you were going with your several questions/thought experiments. The bottom line is that if you’ve calibrated your refractometer at a certain temperature, then you should use it near that temperature. So since I think the norm would be to have it calibrated at room temperature, if you store your water someplace cold or hot, you bring out of the tank or storage area into the room-temperature room and measure at that temp.

Automatic temperature correction on refractometers is very helpful, it will make it so that you don’t need to worry about your exact temperature as long as you are not calibrating vs testing in markedly different temperatures.

Regarding temp and salinity measurement (reinforcing what was already said)- Colder water fundamentally has a higher refractive index (reads higher salinity on a refractomer) without actually having a higher salinity. Not to be confused with the issue of how much salt can dissolve into water of different temperatures, which is a totally different issue but is easy to confuse. There is a negligible change to actual salinity at different (reasonable) temps. So if you make up water to 35 ppt at room temp, it will still be 35 ppt when you add it to your tank and it warms up.
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John- am not totally sure what's bothering you. But yes, this is a good summary of the earlier posts.
Cheers
 
ofzakaria said:
So if I measure a 35ppt water after heating it to 90 degree using a perfectly calibrated refractometer. You think it will read 35ppt?


Did you read the material I included? The pdf is about lab grade salinity measurments equipment which has circuits for temp compensation yet they will say you better do the measurment in 25c.
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Yes, I read it.
If you want some super accurate laboratory number, then sure, you need to do that, and also likely use a better light source,
and make sure optics are properly covered with few bubbles, and do multiple readings, and clean things well, and so on.

But remember:
With our normal hobby grade refractometers, it is hard to even see +/-1 on the indicator lines.
And our temp swings are maybe 20 deg.
Given that, the little temp compensator inside should be sufficient to keep temp issues in line with other innacuracies.
 
rygh said:
Yes, I read it.
If you want some super accurate laboratory number, then sure, you need to do that, and also likely use a better light source,
and make sure optics are properly covered with few bubbles, and do multiple readings, and clean things well, and so on.

But remember:
With our normal hobby grade refractometers, it is hard to even see +/-1 on the indicator lines.
And our temp swings are maybe 20 deg.
Given that, the little temp compensator inside should be sufficient to keep temp issues in line with other innacuracies.
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Well spoken and agreed.
I struggled with salinity for a while when I started mixing in the garage. Temp swing was big and always suspected if my measurments are not accurate. My fear was large errors thats why I kept chasing what can introduce such..
Thanks for the input, was fun discussion!
 
I have yet to calibrate my refractometer, but occasionally check with rodi and store bought NSW. Always on point

They one thing most folks forget is to clean and ensure the hinges are smooth. That will impact your readings if not
 
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