Does your calibration solution need calibrated?

[jason2459]

One of the very basic parameters that we need to maintain is that of salinity which can directly and indirectly effect all other parameters.

http://reef2reef.com/threads/optima...-reef-aquarium-by-randy-holmes-farley.173563/


Being able to accurately test for and read what that salinity is can be challenging. There's many methods to be able to determine what your aquarium or new saltmix salinity is at.

http://reef2reef.com/threads/salinity-determination-by-density.238209/



For many years I've used many different devices including different probes, many different refractometers, digital refractometers, floating hydrometers, and even swing arm hydrometers.

All need and should at least be checked for calibration and if possible calibrated periodically and properly.

Refractometers and Salinity Measurement
http://www.reefedition.com/refractometers-salinity-measurement/


I've used in the past a few different calibration solutions. It's important to know though that sometimes they are not accurate. Either when you first get them if bought pre-made or over time with any kind you have due to potential evaporation.

When purchasing I usually buy two to cross check each other. Usually there's a very slight and acceptable variation. Sometimes though there's large discrepancies. In the past 10 years or so I've maybe have had 3 or 4 bad bottles of calibration fluid sent to me.

Add one more to that count.


In comes the home brew calibration vs store bought

Article worth repeating
Refractometers and Salinity Measurement
http://www.reefedition.com/refractometers-salinity-measurement/

In there is how to make your own solution.

I used canning and pickling salt as its only ingredient is salt (sodium chloride). Some kosher salts will work too. Morton's Kosher salt has an anti-caking agent in theirs. Used RO/DI for the water to mix the salt in.

I also picked up that bottle as it mixes up the 2L volume version easily (I still used my cylinder and scale)and the bottle keeps sealed from evaporation even when pouring a tiny bit out for use. It has a pop top for drinking

After mixing up here's the DIY calibration solution readings (used my digital refractometer for easy reading for this post. It was just calibrated to 0 with RO/DI.)

New bottle of 35ppt calibration solution.

And its reading

Not good. So, I added some RO/DI to bring it to 35ppt and realized why when I have 2L of perfectly good calibration solution I just made and tossed the small bottle out.

 

[ritter6788]

I have 2 bottles of calibration solution from 2 different companies and they don't read the same. It's not way off but just goes to show you the standards can't always be trusted. Just because there is a company name on it doesn't mean it's accurate.

 

[Battlecorals Verified Sponsor]

Funny. I just did this today myself with a fresh bottle of pinpoint and got the same reading. On my Milwaukee I had never checked against a standard but do calibrate it fairly often with rodi

So the pinpoint is that off then you think?

 

[ritter6788]

I just calibrated mine with RO/DI and tested with my calibration solution.

That bottle is a few years old.

 

[jason2459]

Funny. I just did this today myself with a fresh bottle of pinpoint and got the same reading. On my Milwaukee I had never checked against a standard but do calibrate it fairly often with rodi

So the pinpoint is that off then you think?

Yes it was that off. My probe and optical refractometer both read it very high.

Edit: to clarify, that particular bottle was high. I've had many over the years that were just fine.

 

[jason2459]

I just calibrated mine with RO/DI and tested with my calibration solution.

That bottle is a few years old.

That's not to bad and could be accurate and either way good enough. Unfortunately, with the Milwaukee digital it doesn't have quite the resolution to know where that really is. It could be rounding up or down. One reason I don't mainly use the Milwaukee and why I like my probe and refractometer. Where I can see if it's a hair over 35.5 which the Milwaukee will round up to 36 or a hair under 35.5 and the Milwaukee would round down to 35. With the probe being even higher resolution.

 

[dbl]

That little bottle of Pinpoint calibration nearly drove me mad. I ended up tossing it because it just didn't make any sense. I'm glad to see I'm not the only one that was/is struggling with it. Thanks so much for sharing.

 

[JimWelsh]

I could be mistaken, but I don't believe that the Pinpoint conductivity standard is valid to use to calibrate a refractometer. The two devices are measuring salinity using very different properties (conductivity vs. refractive index). The Pinpoint standard is most likely simply a KCl solution of the correct concentration to have the correct conductivity at the stated temperature. That has absolutely nothing to do with what its refractive index is, which is what you're measuring with the refractometer. Apples and Oranges. FWIW, you should NOT expect to be able to use the NaCl refractometer calibration standard to calibrate your Pinpoint salinity probe, either, and I would not be at all surprised if the 35 PPT NaCl standard read something significantly different from 35 PPT when measured with a properly calibrated salinity probe.

 

[Randy Holmes-Farley Verified Community Expert]

I could be mistaken, but I don't believe that the Pinpoint conductivity standard is valid to use to calibrate a refractometer. The two devices are measuring salinity using very different properties (conductivity vs. refractive index). The Pinpoint standard is most likely simply a KCl solution of the correct concentration to have the correct conductivity at the stated temperature. That has absolutely nothing to do with what its refractive index is, which is what you're measuring with the refractometer. Apples and Oranges. FWIW, you should NOT expect to be able to use the NaCl refractometer calibration standard to calibrate your Pinpoint salinity probe, either, and I would not be at all surprised if the 35 PPT NaCl standard read something significantly different from 35 PPT when measured with a properly calibrated salinity probe.

I was concerned about that too, but Lou Dell of American Marine told me it was a seawater mimic, not just a conductivity solution, so should be good for most methods.

 

[jason2459]

Yep, I've used the pinpoint solution for years and have matched up well testing salt mixes cross checked with my probes both pin point (of course calibrated with the same solution)., apex probe (calibrated with their solution),Triton calculated est based on @JimWelsh spreadsheet, and my digital refractometer(calibrated with RO/DI.

I have not tested the NaCl solution with the probes yet to know if they test it to 53mS. Like you I don't think they will? At least not the apex probe. @Randy Holmes-Farley ?

 

[Randy Holmes-Farley Verified Community Expert]

Yep, I've used the pinpoint solution for years and have matched up well testing salt mixes cross checked with my probes both pin point (of course calibrated with the same solution)., apex probe (calibrated with their solution),Triton calculated est based on @JimWelsh spreadsheet, and my digital refractometer(calibrated with RO/DI.

I have not tested the NaCl solution with the probes yet to know if they test it to 53mS. Like you I don't think they will? At least not the apex probe. @Randy Holmes-Farley ?

A sodium chloride solution cannot match any two of SG, conductivity, or refractive index. It is slightly different for all three. I show recipes for each using NaCl here:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-06/rhf/index.htm

from it:

Interpolating between these data points suggests that a solution of 3.65 weight percent sodium chloride has the same refractive index as S=35 seawater, and can be used as an appropriate standard (Table 2).

...

Interpolating between these data points suggests that a solution of 3.714 weight percent sodium chloride has the same specific gravity (and density) as S=35 seawater, and can be used as an appropriate specific gravity standard (Table 5). For most purposes, 3.7 weight percent is accurate enough.

...

Without going into detail about how they were measured, the data from these papers indicate that a 53 mS/cm conductivity solution is provided by a 33.64 g/L (0.576 M) sodium chloride solution. That solution corresponds to 3.29 weight percent sodium chloride.2

 

[jason2459]

Thanks Randy. I'd forgotten about that article. I've always referenced the one I linked to.

 

[Randy Holmes-Farley Verified Community Expert]

You're welcome.

 

[rovster]

I've had a bad bottle of calibration solution. Was reading 38 on my digital meter. Crossed with my existing solution. BRS sent me a new one and that one agreed with the old one. Coincidentally it was Pinpoint Solution. Thanks for posting this!

 

[patsheridan]

So here's my question: wouldn't it make sense to calibrate the refractometer to 0 using RoDi water?

 

[rovster]

Read the articles posted and you'll see why calibrating with solution is preferred.

 

[Randy Holmes-Farley Verified Community Expert]

So here's my question: wouldn't it make sense to calibrate the refractometer to 0 using RoDi water?

Depends on the refractometer, Unfortunately, many sold to the hobby are not true seawater refractometers (those types always make that claim), but are made to test sodium chloride brines.

Hence, even if made perfectly, they will necessarily be off when measuring seawater.

OTOH, any refractometer will be correctly calibrated for measuring seawater when using an accurate seawater standard.

 

[Nebraska Reef]

So the point here is to make a new, known standard to replace the potential for error, or is it to check my calibration fluid?

How often is calibration advisable?

 

[Randy Holmes-Farley Verified Community Expert]

So the point here is to make a new, known standard to replace the potential for error, or is it to check my calibration fluid?

How often is calibration advisable?

Depends on the type of device, and the exact device. a hydrometer may just need to be checked once. A refractometer and conductivity probe may need it more or less often, and you just need to see how much yours seems to drift. My conductivity meter never drifted at all.

Any time you are about to take an action based on an unusually high or low reading, recalibrate first.

You can get two or more standard from different suppliers, or make your own if you are concerned about the accuracy of one solution.

 

[jason2459]

So the point here is to make a new, known standard to replace the potential for error, or is it to check my calibration fluid?

How often is calibration advisable?

For me it was to check the calibration fluid. In the past I normally get two different bottles to cross check for accuracy like Randy just mentuoned. This one I didn't and got just one bottle. Being that it was so far off I knew right away the solution was wrong. Then I made up the DIY NaCl standard to check. Going forward I'll probably stick to the DIY standard especially since this 2L bottle will last me a very long time.

I don't normally have to callibrate very often anymore since getting better quality measurement devices. Using the cheap $30 refractometers I would have to callibrate often. Red Sea's refractometer was amazingly even worse. My veegee/vitasine is the best one I've used so far for keeping calibration and ease of reading.