calibrating refractometer

[saltybob]

Got some pinpoint salinity monitor 53.0ms calibration fluid. Calibrated that to 35ppt. 1.025. Then did some distilled water a little later and it was all the way at the bottom before zero. So my question is what to trust more? Go by the distilled water or the pinpoint fluid? Thanks)

 

[uneverno]

Temperature of the sample is a factor in the equation. I.e. the distilled and salt water should be the same temp when you calibrate. Preferably, the temp you keep your tank at.
Any future tests of aquarium water must be performed at the same temp as the calibration sample, otherwise your salinity readings may be off. I could well be wrong, but that's how I understand the process.

 

[saltybob]

mmm did not know that=) For sure the calibration solution and the distilled water were colder than the tank. So pretty much warm the solution and the distilled to the same temp as my tank. But if the refractometer has temp compensation do you still need to do this?

 

[xcali1985]

Originally Posted by saltybob
http:///forum/post/3086643
mmm did not know that=) For sure the calibration solution and the distilled water were colder than the tank. So pretty much warm the solution and the distilled to the same temp as my tank. But if the refractometer has temp compensation do you still need to do this?
What I do is take a small amount of distilled water and a small amount of tank water and let them sit in a cup for a while then calibrate it with the Distilled then test the saltwater.
Ive done this then also test the tank water which was only about 3 degrees warmer and salanity has been as much as 2 points off just by that little change.
The little guide that came with my refracto say to recalibrate if more than 5 degrees. The best way to be accurate is to get both samples the same.

 

[number1gsxxr]

My calibration solution says it's 1.025 @ 77 degrees F. Since most tanks are a bit higher, ideally it would be better to let the tank water cool to 77 and then read from the refractometer? Assuming you already calibrated the refractometer with the solution at 77.
You wouldn't be able to raise the temp of the solution to match the tank because then you wouldn't know what the salinity of the calibration solution is?

 

[bionicarm]

Most of the refractometers I've owned have an Automatic Temperature Adjustment. I calibrate mine with my RO/DI water. It has zero pollutants in it, and it's what I use to fill my tank. Been doing this for years with no ill affects on my tank inhabitants.

 

[chaseter]

Finally! I can answer a question!
When you use a refractometer, be sure that your sample is fully mixed. So, if you are leaving out a sample of salt water, the salt particles can move towards the bottom of the sample because NaCl is heavier than H2O, which would give you a false reading if you take a reading off the top. Salt water in your tank and in the ocean is constantly mixing and moving. So, if you take a reading right out of your tank, it would be fine.
Just properly mix your sample before using a refractometer by stirring.

 

[bang guy]

Yep, the calibration fluid is the best way. I won't say that temperature is irrelevant but if everything is a reasonable temperature then the effect if temperature on Salinity is tiny.

 

[zippgirl]

I am most likely wrong here, but I thought the calibrating fluid was suppose to come to 36 ppt (1.026), which might make your distilled water come up right, if it wasn't set for 1.025. But I'm not sure though, just thought I read it some where. I bought some calibration fluid and checked mine and came up to exactly 1.026, so please let me know if I am wrong.

 

[bang guy]

Originally Posted by zippgirl
http:///forum/post/3088255
I am most likely wrong here, but I thought the calibrating fluid was suppose to come to 36 ppt (1.026), which might make your distilled water come up right, if it wasn't set for 1.025. But I'm not sure though, just thought I read it some where. I bought some calibration fluid and checked mine and came up to exactly 1.026, so please let me know if I am wrong.
1.026 is a specific gravity reading. specific gravity isn't really measured by a refractometer, they measure salinity.
There are different calibration solutions but 53ms is a common one and it should read 35ppt on a refractometer.