Salinity, Temp, and Refractometer

[rffanat1c]

Ok so I have googled the daylights out of this and am still a bit confused. I understand temp and salinity have a relationship when it comes to Sg. I know ppt relates to how much salt is in water. I know ATC refers to the instrument itself regarding its environment. My question IS....since the refractometer adjusts for the temp it is in, does that mean if I test water at the same temp the Sg reading is accurate?

I keep my NSW in a trash can and it is at 65 degrees. Refractometer is kept right next to it. If I add this water to my tank (78 degrees) will I throw off my salinity. Refractometer is a Milwaukee Digital.

 

[RobZilla04]

Shouldn't throw it off that much to matter IMO. You can always take a cup of the NSW from the 65 degree environment and let it adapt to 78ish degrees and retest.

If my memory serves me right, the advise is to allow warmer water to sit on the refractometer for 45 seconds to allow the temp to stabilize.

 

[JP Reef]

The salinity doesn't actually change when temperature changes. Temperature affects the instrument you are using to measure as the density of the water changes. That is why you should always wait some time for your refractometer to adjust to the temp. Allow the temperature to steady.

I would calibrate it at the temperature you use it, and wait a minute before reading any samples.

 

[sjadet]

I always take some RODI water at room temp and set salinity to 0 before testing the tank water.


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[Vinny Kreyling]

Testing with RO is not that accurate.
The closer you calibrate to natural saltwater the better it will read.

 

[BrettDS]

As others have said, the temperature affects the reading and the refractometers that offer ATC give you accurate readings no matter what the *ambient* temperature is (as long as it's not at the extremes).

The small amount of water that you put on a refractometer will quickly match the temp of the refractometer (the Milwaukee manual says to wait about a minute if there is a large temp differential between the water you use and the instrument) so it's really the temperature of the refractometer that maters and not the water temp.

But as long as you're using an instrument with ATC and the instrument is stored at a moderate temp then you can trust the reading

 

[rffanat1c]

Ok thanks. They both are at 65 degrees so it is within range of the ATC


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[BaleKlocoon]

rffanat1c,

The temperature will not affect the amount of salt that it is in your water as others have mentioned, but it does change the specific gravity of the liquid which is a method of estimating salinity. This is because water expands and contracts slightly with temperature.

The specific gravity of seawater is 1.0269 at 60 degrees F and 1.0266 at 77 degrees F. Don't worry about the temperature of the water in your tank, worry about the temperature the sample of water becomes after it is dropped on your refractometer.

If you keep the temperature of your house at 60 degrees, and your refractometer is in your house, your refractometer is 60 degrees. When you put a few drops of tank water on the refractometer, your sample will eventually become 60 degrees. I would wait a minute or so. In this example you should be aiming for the 1.0269 number. It doesn't matter what the temperature of your tank water is.

This is just an example. 1.0269 might not be the number you want, and your house might not be 60 degrees. Personally, I cannot read my refractometer that precisely so I just aim for the 1.025 to 1.026 range regardless of temperature.

 

[rffanat1c]

rffanat1c,

The temperature will not affect the amount of salt that it is in your water as others have mentioned, but it does change the specific gravity of the liquid which is a method of estimating salinity. This is because water expands and contracts slightly with temperature.

The specific gravity of seawater is 1.0269 at 60 degrees F and 1.0266 at 77 degrees F. Don't worry about the temperature of the water in your tank, worry about the temperature the sample of water becomes after it is dropped on your refractometer.

If you keep the temperature of your house at 60 degrees, and your refractometer is in your house, your refractometer is 60 degrees. When you put a few drops of tank water on the refractometer, your sample will eventually become 60 degrees. I would wait a minute or so. In this example you should be aiming for the 1.0269 number. It doesn't matter what the temperature of your tank water is.

This is just an example. 1.0269 might not be the number you want, and your house might not be 60 degrees. Personally, I cannot read my refractometer that precisely so I just aim for the 1.025 to 1.026 range regardless of temperature.

Thanks


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