I'M STUMPED! Does temperature affect salinity?

j.falk

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I mix my water in a Brute trash can in the basement. I use a heater to get the temp right and a water pump to mix the salt into the water. I always mix my water for 24 hours before using it.

Today I checked the salinity of the water in the Brute and it came to 1.023. Then I checked my tank salinity...1.025. Then I checked the water in the Brute again and now it says 1.020. Here's the kicker...I always test the salinity twice every time I check it so I know the numbers above were correct at the time I tested it. The only difference I can think of between the 1.023 test and the 1.020 test is that I left the lid off of the Brute can when I went upstairs to test the tank water. Because of that I'm assuming the temperature might have dropped a little bit as we are running the air conditioner right now...but would that have an affect on the salinity readings?
 

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Did you check the temp also? I don't know about temp affecting salinity but if it does I have doubts the temp in a full brute container would have dropped in the time it took you to walk up stairs and back :thinking-face:

EDIT:
Screenshot_20230601_102747_Chrome.jpg
 
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j.falk

j.falk

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I did not check the temp in the Brute. It's only a 10 gallon baby Brute. I have a preset heater in there that is set for 80 degrees...but my thermometer I had for it has somehow disappeared and I need to get by the store to get a new one.
 

Jason_MrFrags

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Yes temp has inverse relationship with Salinity. Increase temp causes salinity to decrease. Could of just been a bad reading from whaever your using to measure
 

second_decimal

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Most salinity measuring devices will compensate for temp unless your using a swing arm hydrometer. You should be using a calibrated refractometer with calibration solution.

If the heater is preset to 80°, the tank should be the same temp = same salinity reading. Well, at least temp would not play a role in a different reading.
 

Jay Hemdal

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You’re measuring specific gravity, not salinity. Specific gravity changes a bit with temperature, salinity does not.
That said, that is a larger drop than would be expected with any reasonable temperature rise.
Jay
 
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j.falk

j.falk

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Yes temp has inverse relationship with Salinity. Increase temp causes salinity to decrease. Could of just been a bad reading from whaever your using to measure
That's why I always test 2 times every time I check my salinity. Not sure why the first two tests on the Brute water were 1.023 and the second two tests were 1.020? The only difference between the two tests were the five minutes I walked up to the second floor of the house to check the tank's salinity.
 

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As jay stated, there is a difference with salinity and specific gravity and also in a drum there is precipitation and evaporation as with mine and salt goes up and down. Temperature plays a role.
 
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j.falk

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I'm not sure me using the word salinity vs. specific gravity threw anyone off. It looks everyone who responded knew what I was referring to. :grinning-squinting-face:
 

second_decimal

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Figures a comment would elicit a response of “salinity is not specific gravity” technicality. The 2 convert and are definitely measuring the salt content whether it’s displayed as SG or ppt. There is an unlimited supply of information on this subject on the web. In any event, it doesn’t really play a role as long as the measurements are taken in the same format.

It could have been a small air bubble on the reading glass of the refractometer. Yes, temperature affects the readings but if the tank and the new water are the same temp, it won’t be the an influencing factor. Again, calibrate and test.
 

Randy Holmes-Farley

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The first post in this thread is uninterpretable since no device or method is reported, and obviously the numbers posted are not the salinity claimed. So what is it?

Let's start with some facts:

1. Salinity cannot ever change with temperature. Salinity is traditionally measured in weight of salt per weight of total water plus salt. Temperature cannot ever change that.

2. Specific gravity also hardly varies with temperature at all. There is NO temperature to specific gravity table of corrections. That is a misunderstanding of tables that are for different conversions. Specific gravity (sometimes called specific density) is usually defined as the ratio of the mass of a volume of sample divided by the mass of the same volume of pure water AT THE SAME TEMPERATURE. Unfortunately, there is no universally recognized temperature to measure and report specific gravity. The sg of 35 ppt seawater is about 1.0278 at 3.98 °C, 1.0269 at 60 °F , 1.0266 at 20 °C, and 1.0264 at 77 °F. Note that the changes between 60 deg F and 77 deg F are small compared to the uncertainty of the devices hobbyists use, and are not the source of issues the OP reports.

3. What does change greatly with temperature are the physical properties that reefers typically use to calculate salinity and report it as salinity or specific gravity. Conductivity, refractive index and density all change a lot with temperature, and in different ways. Many of these devices automatically make corrections for these temperature effects, but some do not.

Obviously, without knowing which device the OP is using, no one can confidently explain what he is observing.
 

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The first post in this thread is uninterpretable since no device or method is reported, and obviously the numbers posted are not the salinity claimed. So what is it?

Let's start with some facts:

1. Salinity cannot ever change with temperature. Salinity is traditionally measured in weight of salt per weight of total water plus salt. Temperature cannot ever change that.

2. Specific gravity also hardly varies with temperature at all. There is NO temperature to specific gravity table of corrections. That is a misunderstanding of tables that are for different conversions. Specific gravity (sometimes called specific density) is usually defined as the ratio of the mass of a volume of sample divided by the mass of the same volume of pure water AT THE SAME TEMPERATURE. Unfortunately, there is no universally recognized temperature to measure and report specific gravity. The sg of 35 ppt seawater is about 1.0278 at 3.98 °C, 1.0269 at 60 °F , 1.0266 at 20 °C standard, and 1.0264 at 77 °F. Note that the changes between 60 deg F and 77 deg F are small compared to the uncertainty of the devices hobbyists use, and are not the source of issues the OP reports.

3. What does change greatly with temperature are the physical properties that reefers typically use to calculate salinity and report it as salinity or specific gravity. Conductivity, refractive index and density all change a lot with temperature, and in different ways. Many of these devices automatically make corrections for these temperature effects, but some do not.

Obviously, without knowing which device the OP is using, no one can confidently explain what he is observing.

That's interesting. So is the below true, then:

1. Refractometers and conductivity probes would be affected.
2. Salinity readings from basic swing arm hydrometers and also floating hydrometers would not be affected.
 
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j.falk

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The first post in this thread is uninterpretable since no device or method is reported, and obviously the numbers posted are not the salinity claimed. So what is it?

Let's start with some facts:

1. Salinity cannot ever change with temperature. Salinity is traditionally measured in weight of salt per weight of total water plus salt. Temperature cannot ever change that.

2. Specific gravity also hardly varies with temperature at all. There is NO temperature to specific gravity table of corrections. That is a misunderstanding of tables that are for different conversions. Specific gravity (sometimes called specific density) is usually defined as the ratio of the mass of a volume of sample divided by the mass of the same volume of pure water AT THE SAME TEMPERATURE. Unfortunately, there is no universally recognized temperature to measure and report specific gravity. The sg of 35 ppt seawater is about 1.0278 at 3.98 °C, 1.0269 at 60 °F , 1.0266 at 20 °C, and 1.0264 at 77 °F. Note that the changes between 60 deg F and 77 deg F are small compared to the uncertainty of the devices hobbyists use, and are not the source of issues the OP reports.

3. What does change greatly with temperature are the physical properties that reefers typically use to calculate salinity and report it as salinity or specific gravity. Conductivity, refractive index and density all change a lot with temperature, and in different ways. Many of these devices automatically make corrections for these temperature effects, but some do not.

Obviously, without knowing which device the OP is using, no one can confidently explain what he is observing.
A standard ATC refractometer.

1200px-2020_Refraktometr.jpg
 

Randy Holmes-Farley

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That's interesting. So is the below true, then:

1. Refractometers and conductivity probes would be affected.
2. Salinity readings from basic swing arm hydrometers and also floating hydrometers would not be affected.

Refractometers can have automatic temperature compensation, or not, depending on the device design.

Conductivity meters used by hobbyists most often have temperature corrections built in, but not all conductivity devices do it, and many would not have the exact correction for seawater.

Floating glass hydrometers have no built in way to correct for temp changes. Tables are usually necessary to convert the hydrometer reading to other units of measure, such as specific gravity or salinity.

Swing arm hydrometers do have a built in correction based on the materials used, and it seemed pretty good when I tested some, but may not always be accurate in the first place.
 

Randy Holmes-Farley

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A standard ATC refractometer.

1200px-2020_Refraktometr.jpg

Assuming it is designed and functioning properly and is within its ATC temperature range, the result should not vary as the sample temperature is changed.

The changes observed may be random errors, or imperfect ATC correction.
 
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j.falk

j.falk

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Assuming it is designed and functioning properly and is within its ATC temperature range, the result should not vary as the sample temperature is changed.

The changes observed may be random errors, or imperfect ATC correction.
Thank you for your insight.

One thing I do (and I'm not sure if this would affect the refractometer or not) is I wipe the lens off with my tshirt after testing. Could the lens be damaged or altered from wiping it with cotton material? I wouldn't think so, but it is something I considered after today's readings.
 

Randy Holmes-Farley

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Thank you for your insight.

One thing I do (and I'm not sure if this would affect the refractometer or not) is I wipe the lens off with my tshirt after testing. Could the lens be damaged or altered from wiping it with cotton material? I wouldn't think so, but it is something I considered after today's readings.

That wiping is not likely the issue, but a soft cloth (like a glasses microfiber) would be better.
 

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