calibrating a refractometer

[clownlover]

very mysterious josh. my stingy sense is tingling.

 

[clownlover]

I calibrated my refrato with RODI, and used it for about 3 years that way. I recently calibrated it with calibration fluid and it was 12ppt off. Yes, my refractometer said it was 47ppt instead of 35ppt. So when I was mixing up water to what I thought it was 35ppt, it was actually 23ppt (1.019!)

which would explain why my corals are dying...

B

i hav a feeling im doing the same thing. my floating hyrdo is 5ppt different from my fract. would explain my zoos melting i think.

 

[rgun2515]

liveaquaria.com is replacing the unit. Tested with their support line last night and they want to change it out.

I will post an update after I get the new one and test.

Link from "Fragmented" http://reefkeeping.com/issues/2006-12/rhf/index.php is right on. That's exactly what was happening. The new device they sent is the same. In this case, the hydrometers were correct. You can't calibrate "MY type" of refractometer with RO/DI.

This is mine-
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=10490

And this is required to calibrate-
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=18718

 

[Chiefmcfuz]

Come to the swap it's educational as well!

 

[vanceny]

I made the standard from the article and my refractometer was reading about 3ppt higher than it should. Here's how to make it:

To make a 3.29 weight percent sodium chloride solution, dissolve 1 teaspoon (6.20 grams) of Morton's Iodized Salt in 182 mL (182 g) of freshwater (making a total volume of about 184 mL after dissolution of the salt). This solution can be scaled up as desired.
For a rougher measurement in the absence of an accurate water volume measurement:

1. Measure ? cup of Morton's Iodized Salt (about 73.1 g)
2. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified freshwater (about 2104.4 g)
4. Add 3 tablespoons of purified freshwater (about 45 g)
5. Dissolve the total salt (73.1 g) in the total water volume (2149.4 g) to make an approximately 3.29 weight percent solution of NaCl. The volume of this solution is larger than the Coke bottle, so dissolve it in another container.
​

[[Notice added post-publication: the standards described here that use Coke bottles are subject to variation in the volume of a 2-L Coke bottle. It has recently come to my attention that such 2-L bottles can vary in total volume, and that this can lead to at least a 1 ppt error in the salinity of the standards matched to seawater salinity of 35 ppt. Standards made with accurate measurements of salt and water should still accurately match 35 ppt.]]

I have a scale so I used the weighted amounts instead of the rough estimates based on volume.

 

[clownlover]

I made the standard from the article and my refractometer was reading about 3ppt higher than it should. Here's how to make it:

To make a 3.29 weight percent sodium chloride solution, dissolve 1 teaspoon (6.20 grams) of Morton's Iodized Salt in 182 mL (182 g) of freshwater (making a total volume of about 184 mL after dissolution of the salt). This solution can be scaled up as desired.
For a rougher measurement in the absence of an accurate water volume measurement:

1. Measure ? cup of Morton's Iodized Salt (about 73.1 g)
2. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified freshwater (about 2104.4 g)
4. Add 3 tablespoons of purified freshwater (about 45 g)
5. Dissolve the total salt (73.1 g) in the total water volume (2149.4 g) to make an approximately 3.29 weight percent solution of NaCl. The volume of this solution is larger than the Coke bottle, so dissolve it in another container.
​

[[Notice added post-publication: the standards described here that use Coke bottles are subject to variation in the volume of a 2-L Coke bottle. It has recently come to my attention that such 2-L bottles can vary in total volume, and that this can lead to at least a 1 ppt error in the salinity of the standards matched to seawater salinity of 35 ppt. Standards made with accurate measurements of salt and water should still accurately match 35 ppt.]]

I have a scale so I used the weighted amounts instead of the rough estimates based on volume.

and then i use this solution to calibrate my fract to 35ppt right??

 

[vanceny]

Yes. Take a few drops and calibrate to 35ppt. I did this a few times to make sure it was reading the same each time.

 

[Josh]

Or just bring the refractometer to the swap and have it calibrated in style!

 

[Aqua Pro Builder]

I am bringing my refractometer to compare too.

 

[clownlover]

def doin both.

 

[clownlover]

just did the test. i used a scale to get exact measurments. the tank was at 40ppt

 

[clownlover]

also, how long will that solution last?

 

[prattreef]

the solution won't go bad, but if any evaporation occurs it will throw things off as might imagine. I'd seal it as well as possible and mark the vial so you can tell if evaporation has occurred.

 

[Djay]

this is good info to know, now let me go calibrate my meter

 

[Aqua Pro Builder]

How do you calibrate your refractometer? With RO/DI water? I heard this and did it. Now the refractometer says my the specific gravity is 1.027? I have two hydrometers. One says 1.0235 and one says 1.023. Before I tried to calibrate the refractometer with RO/DI water, it said 1.024.

All tests done with the same sample.

If you use calibration solution and think that's how it should be done, where around here (Westchester/Bronx) can I pick some up?

If the complex tool like refractometer does not come with proper instructions, your Hydrometer could be more reliable in this case. :tongue1:

 

[EmilyT]

Hooray for tedious thread prevention fluid! :party: