4 instruments 4 different salinity readings...What is my actual salinity?

[Randy Holmes-Farley Verified Community Expert]

Randy I just noticed you did an article on refratometers. I just looked at it. I appreciate the amount of effort you put into it, I enjoyed it nice work!

Glad you liked it!

Happy Reefing.

 

[exnisstech]

34.4 and 35.3 are very close. I'd trust either #1 or #2.

This is just my opinion, but it's unfortunate that the hobby has coalesced around refractive index as the default method to measure salinity. I've never had a refractometer that wasn't a hassle to use or keep calibrated. In my experience, drop-in measuring tools like the hydrometer above or conductivity meters are not much more expensive than quality refractometers and give much more reliable readings.

While I'm sure this is correct refractometers are so much easier to use IMO. I've been using the same one for years and rarely need to adjust the calibration. I check it with Randy's fluid. Hydrometers are for people with sure hands that don't drop things. That's a skill set I do not have.

 

[Miami Reef]

I'd check all of them, including the glass hydrometer, in a known standard (DIY or high end commercial) designed for each device, if I wanted to have confidence in them.

After reading this post, I decided to check my Tropic Marin Hydrometer. I assumed it was very reliable, but I wanted to make a standard for fun.

To produce a 3.714 weight percent sodium chloride solution, dissolve 1 teaspoon (6.20 grams) of Morton's Iodized Salt in 161 mL (161 g) of freshwater (making a total volume of about 163 mL after dissolution of the salt). This solution can be scaled up as desired.

https://reefkeeping.com/issues/2004-06/rhf/index.php

^ That recipe is for specific gravity standards, there are other salinity standard recipes in that link.

Anyway, I got my 500mL +/-5mL graduated cylinder. I added 450 mL of RO/DI.

I added 17.30g of Mortons Iodized Salt. Stirred it with a magnetic stirrer.

The results? After temperature compensation, I got 1.0267.


Very nice.

Disclaimer, although my device was accurate, it does not necessarily mean yours will/will not be. Each person should ideally test their device in a known standard. These are handmade tools.

 

[Randy Holmes-Farley Verified Community Expert]

While I'm sure this is correct refractometers are so much easier to use IMO. I've been using the same one for years and rarely need to adjust the calibration. I check it with Randy's fluid. Hydrometers are for people with sure hands that don't drop things. That's a skill set I do not have.

Refractometers are not easier to use than a good conductivity meter, but I agree they may be easier than very large floating hydrometers.

 

[Randy Holmes-Farley Verified Community Expert]

After reading this post, I decided to check my Tropic Marin Hydrometer. I assumed it was very reliable, but I wanted to make a standard for fun.

https://reefkeeping.com/issues/2004-06/rhf/index.php

^ That recipe is for specific gravity standards, there are other salinity standard recipes in that link.

Anyway, I got my 500mL +/-5mL graduated cylinder. I added 450 mL of RO/DI.

I added 17.30g of Mortons Iodized Salt. Stirred it with a magnetic stirrer.

The results? After temperature compensation, I got 1.0267.


Very nice.

Disclaimer, although my device was accurate, it does not necessarily mean yours will/will not be. Each person should ideally test their device in a known standard. These are handmade tools.

Thanks for testing. Not many folks do, and just assume they are accurate.

 

[KStatefan]

After reading this post, I decided to check my Tropic Marin Hydrometer. I assumed it was very reliable, but I wanted to make a standard for fun.

https://reefkeeping.com/issues/2004-06/rhf/index.php

^ That recipe is for specific gravity standards, there are other salinity standard recipes in that link.

Anyway, I got my 500mL +/-5mL graduated cylinder. I added 450 mL of RO/DI.

I added 17.30g of Mortons Iodized Salt. Stirred it with a magnetic stirrer.

The results? After temperature compensation, I got 1.0267.


Very nice.

Disclaimer, although my device was accurate, it does not necessarily mean yours will/will not be. Each person should ideally test their device in a known standard. These are handmade tools.

Mine was 0.0002 off when I measured 450 ml of water in my graduated cylinder then I purchased a 500 ml volumetric flask and it was right on.

 

[Miami Reef]

Mine was 0.0002 off when I measured 450 ml of water in my graduated cylinder then I purchased a 500 ml volumetric flask and it was right on.

Nice. The graduated cylinder isn’t very accurate, but I ensured the meniscus was lined up exact. The temp used was cooler, so maybe that played a role?

Nevertheless, this tool is much more accurate than most reefing salinity measurements. I was happy with my results.

 

[Sleeping Giant]

how I test my salinity

 

[Randy Holmes-Farley Verified Community Expert]

Nice. The graduated cylinder isn’t very accurate, but I ensured the meniscus was lined up exact. The temp used was cooler, so maybe that played a role?

Nevertheless, this tool is much more accurate than most reefing salinity measurements. I was happy with my results.

True story...

I was an undergraduate chem/bio major working in a biochemistry lab for my senior thesis. As the low man on the totem pole, I also had to do some grunt work for the lab in general.

One day they started a large procedure to purify a specific enzyme out of spinach leaves. My lowly job was to make various buffer solutions for the project.

I was happily rolling along a few days into the procedure when a more senior team member came by and asked what I was doing. I said I was making more of the buffer for the procedure.

Uh, he said, how did you measure the water volume?

i just filled the erlenmeyer flask up to the 250 ml line, I said.

Uh oh, did you do that for the previous batch?

Yes, I said, starting to worry.

Well, he said, you better hope this batch of enzyme works out or James (cannot recall his actual name, but the post doc leading the preparation) is going to be furious and blame you if it goes bad.

Such was my introduction to the world of liquid volume measurement using various pieces of glassware.

Erlenmeyer flasks and beakers are on the bottom in terms of accuracy. Accuracy is often +/- 10%.

Graduated cylinders are pretty good and in the middle of the pack. They can be class A or class B. Accuracy depends on volume. For 1 L, class A is +/- 0.3% and class B is 0.6%. For 10 mL, class A is 1% and class B is 2%.

Specific single volume volumeteric flasks are the best. They can be class A or class B. Accuracy depends on volume. For 1 L, class A is +/- 0.03% and class B is 0.06%. For 10 mL, class A is 0.2% and class B is 0.4%.

End of my story, the prep was among the best ever, and the guy who knew my secret did not feel the need to tell the rest of the team what I had done.