New Salinity Stds.

Randy and I have been working on some new salinity stds. Based on the data I found for him he has come up with new numbers. The old numbers were to low. ie, the new 3.65 use to be 3.6 and the 3.17, is now 3.28 and the 3.714 was 3.7


Salinity Standards

Here's a compilation of salinity standards that people can make out of dry table salt and water (using a good balance):

If you want an S=35 standard for specific gravity, try 3.714 weight percent NaCl in water at 20 deg C

If you want an S=35 standard for refractive index, try 3.65 weight percent NaCl in water

If you want an S=35 standard for conductivity, try 3.28 weight percent NaCl in water

Some will ask what is a weight % ;



So.....


3.28 % = 96.7 ml of water and 3.28 grams of NaCl
Or add 80 ml of water to a graduated container, then add 3.28 g of NaCl. Once dissolved then add water to the 100 ml mark. Or if you will, 96.7 g of water and 3.28 g of NaCl

 

Ummmm! Yep! OK!

Could somebody please explain? Pleeeeeeeease!

John

 

I know from previous discussions that when my refractometer tells me I'm at 1.025, I'm actually low by .001 at 1.024. I'm always hoping to run in the 1.025 to 1.026 range as most test kits are calibrated for 35 ppt and I want my tests to be accurate.

However, If I'm calibrating my refractometer using the new standards, is there a specific purity level of table salt I should use? Morton's is iodized....will that interfere with my self-calibration or should I get a non-iodized salt?

 

Inwall

Morton's is iodized....

That is fine, the Iodine is so small it will have a nil affect. Randy did some test on it

After looking at more data and Randy doing some more tests on RI (Refractive Indexs), it is low by .0015. If we want the tank to be at NSW Salinity of 35 ppt, the refract needs to read 3.65 to = 3.5 NSW. The thing with the calibration solution is you can recalibrate it to this std, so now when it reads 3.5 it is = 3.5 NSW

John

What is it you want explained ?

If anyone has problems making a calibration solution just go ask tjhe chemist at the drug store to do it for you

 

Inwall I thought the readings were +.001 if refractometer said 1.024 then it was really 1.025?

 

No...it's the other way around. However, your question gives me the opportunity to share some great info provided by Boomer.

Originally posted by Boomer
Some errors and things to look at to do this correctly

You all should be trying to achieve a Salinity = 35 ppt, not some SG value. That is why there is so much confusion in this hobby about Salinity/SG. You must have a std Salintiy to go by, otherwise all other values don't mean much in a comparison

The SG Scott gave at 1.0245 with a swing arm type hydrometer = 33 ppt. This type along with the SeaTest does not need to be temp compensated for and this must be pointed out. They are self correcting due to the thermal expansion properties of plastic. Floaters are a different issue which all MUST be aware of if you guys are going to do this. Ex; A SeaTest that reads 1.026 @85 F = 35 ppt and the same @ 72 F =35 ppt. This not the same for floaters where you must use a table or calculator to correct for temp. A floater calibrated to 75-77 F would be way off. Tom has not updated his page it needs some corrections, but they are not that big. You can see the temp column is off, use the column that says 75.2 F and not the C column .Here is a new table set to 77 F and 75 F hydrometers. Most LFS Floaters are calibrated to 75 F, only the Tropic Marin is at 77 F, all others as far as I know are at 75 F. It is by far best to use this calculator than the tables, less chance of error.

http://www.wymag.org.uk/simon/salinityhr.htm

Type in the floating hydrometers calibration temp, such as 77 F / 77F, type in the tank temp 78 F (sample temp). Guess the SG, lets go with 1.0255 for the given value, poof... Salinity = 32.750511169433594. Now lets do the same but the tank is at 84 F, all other things are the same = 34.163665771484375.We want to be close as possible to 35 ppt. It doesn't take much to figure out what SG to have to get a salinity of 35 ppt .In our last example 77 F/ 77F, tank at 84 F, it is 1.0255 = 35 ppt. Type that 1.0255 in the reading table and you get 35.00444250. The best floater is the tropic Marin. The swing arm is the new SeaTest. Either of them should be checked against a known std to see how far off they are. Pure water, not really the greatest thing. The SeaTest when right on is bar far the best thing, as long as you remember how to take care of it properly, otherwise it can be a bad thing.

Notes;

IO normally mixes low Ca even at 35 ppt.Usually around 380 or so, has been so for years

Most good 12" floaters and the SeaTest are within ± .001. SeaTest's seem to be off about .001 to low at the get-go, against a std. Hagen Pseudo-Lab 12 " are right on as as is Tropic Marin

Refract.They read about .001 to low right off the shelf, as they are calibrated to a NaCl std and that is not the same as seawater. So to get 35 ppt at any normal temp it should read 1.027 =35 ppt, as 1.027- .001 = 1.026 (corrected) = 35 ppt.