Calibrate your refractometer with calibration fluid!

[kwajtrader]

I figure it’s good to let others learn from my mistakes, so here goes. I couldn’t figure out why nothing I was doing was getting my calcium above 380 and Mg was equally low. I had calibrated my refractometer to zero using RODI water and had my salinity at 1.024. Turns out after recalibrating with 35ppm calibration fluid, I was actually below 1.020. After slowly raising it to 1.026 over the course of a week+, I’m now at 440 Ca and 1400 Mg. By far the least expensive fix since getting into this hobby!

 

[ricky5415]

Thought they recommend us not to calibrate it down to zero

 

[brandonmason]

Be careful with calibration fluid as it expires. I use to only use it to calibrate with. When I set up my 210 (long ago) I calibrated using the fluid and thought I had everything perfect... WRONG All my corals browned out and my clams died. Couldn't figure it out tested and tested. Finally took in a sample and the store showed my salinity at 1.035

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[enderg60]

you should always calibrate using something in the range of what you want to test for.

Why would you measure the height of something by calibrating the length of a foot to zero?

 

[axio]

This has always been a hot debate topic...

I will just say that some brands of refractometers tell you in the instructions to use Calibration fuild and others such as Redsea tell you to only use RODI water to calibrate.

 

[schwaggs]

I think its best to calibrate in the range you are testing. That being said, you do need to use fresh calibration solutions or you risk the danger of being far worse off.

Would be a cool thing to do at club meetings, a sponsor or member provides a bottle of calibration fluid, we all calibrate our refractometers from the fresh bottle of fluid. We could even bring from home, a sample of tank water and any calibration fluids we have to double-check things.

 

[bcavalli]

Great idea.

 

[enderg60]

aXio;1104786 wrote: This has always been a hot debate topic...

I will just say that some brands of refractometers tell you in the instructions to use Calibration fuild and others such as Redsea tell you to only use RODI water to calibrate.

How is that a debate? If a company provides incorrect instructions its not a debate, its wrong. Sorry but any company that tells you to calibrate to zero should be sued. Thats the dumbest thing Ive ever heard.

You should NEVER calibrate ANYTHING to zero. NEVER. You can reset a zero point such as with a scale, but it is not logically possible to calibrate anything to zero.

You can not measure an amount of something by calibrating to a measurement of nothing.

Hell if you calibrate a PH probe using 3ph fluid and use it at 7-9 ph it will be wrong.

Schwaggs;1104787 wrote: I think its best to calibrate in the range you are testing. That being said, you do need to use fresh calibration solutions or you risk the danger of being far worse off.

Would be a cool thing to do at club meetings, a sponsor or member provides a bottle of calibration fluid, we all calibrate our refractometers from the fresh bottle of fluid. We could even bring from home, a sample of tank water and any calibration fluids we have to double-check things.

I actually tested that. I got a bottle of fluid from BRS many years ago and have used maybe 1/4 of it and left the top off a few times, so I got another one a few months ago. Both still read exactly the same.

I calibrate mine every time I use it. Its usually only off if the temp has changed a bunch or I dropped the refectometer.

The bottles are like $8 and last forever. Just buy one for yourself. If you think its off, get another one. $8 isnt gonna break the bank.

 

[lmm1967]

I think calibration means different things to different people.

Our handheld devices probably can't be "calibrated" at home - but they can have their zero point adjusted by turning a screw.

Either way - I have proven to myself that my particular refractometer is accurate whether I adjust to zero using RODI or adjust to 35 using "calibration" fluid.

 

[enderg60]

And that is exactly the kind of nonsense people keep saying that causes problems.

Calibration has one meaning. It means to set a standard scale of measurement. Zeroing out, is setting your range of measurements.

Think about it this way. Take your car speedometer. They are all calibrated at 35-45 mph because thats the speed you are usually at. Take into account different wheel sizes and other aspects that vary, your speedo could measure 1 mph as 0.9 or 1.1. 2 could then be 1.8 or 2.2. They can perfectly accurate at 40 but be off as much as 5 mph past 80 mph like mine is. If you calibrated at 0 mph by the time you hit 70 it would be off by 10 mph. (pulling numbers out my butt but you get the point)

If you calibrate to zero the inherent error will build up making your measurement less accurate. If you calibrate to the range your testing that error is pushed to numbers that are so far out of ideal the error wont matter. (as in salinity of 1.0159 or 1.0157 still means dead coral, but 1.026 or 1.028 could be an issue.)

Remember, arguing with an engineer is like wresting a pig in mud. Eventually you realize they like it!

 

[kwajtrader]

I have to say that I’m always impressed with the level of passion people have related to this hobby. EnderG60’s points are spot on WRT calibration vs. zeroing. I incorrectly assumed that the physics of refractometers would make the measurement predictably linear within a hobby grade of accuracy from zero to 35ppm and that the amount the light would bend relative to the physical scale of my refractometer would be a constant from the zero point (or maybe I didn’t have calibration fluid and read on the ARC that I could zero it with RO/DI water). Again, wrong….

Anyway, given the excitement on this topic, I’ll have to share some of my other screw-ups! Did I mention that some of the first fish I added to my 70g tank 7 years ago were three quarter sized tangs, two hippo tangs and a yellow tang? I’ve long since sold the large hippo tangs and still have a big fat and happy yellow tang, that is strangely trying to mate with one of my clownfish. I’ve been considering selling him here, but I hate to break up the strange but happy couple. Another story for another day…

As for arguing with Engineers, also spot on.

 

[seand]

I'm no engineer but I like to keep my salinity at 1.02615432776589 it's no easy task and requires an eye dropper but the results are undeniable. Some grow and some die, hahahaha.

 

[axio]

Lmm1967;1104800 wrote: I think calibration means different things to different people.

Our handheld devices probably can't be "calibrated" at home - but they can have their zero point adjusted by turning a screw.

Either way - I have proven to myself that my particular refractometer is accurate whether I adjust to zero using RODI or adjust to 35 using "calibration" fluid.

Sorry I just did this same exact thing in my response above...

Should of said...
"Some refractometers have instructions to calibrate with fluid and others only say just use RO Water to zero it out"

And yes you are completely correct. I think a good bit of the confusion is simply misusing the word calibration... I think is thread alone proves that this might be a good topic for a monthly meeting.

 

[FutureInterest]

EnderG60;1104807 wrote: And that is exactly the kind of nonsense people keep saying that causes problems.

Calibration has one meaning. It means to set a standard scale of measurement. Zeroing out, is setting your range of measurements.

Think about it this way. Take your car speedometer. They are all calibrated at 35-45 mph because thats the speed you are usually at. Take into account different wheel sizes and other aspects that vary, your speedo could measure 1 mph as 0.9 or 1.1. 2 could then be 1.8 or 2.2. They can perfectly accurate at 40 but be off as much as 5 mph past 80 mph like mine is. If you calibrated at 0 mph by the time you hit 70 it would be off by 10 mph. (pulling numbers out my butt but you get the point)

If you calibrate to zero the inherent error will build up making your measurement less accurate. If you calibrate to the range your testing that error is pushed to numbers that are so far out of ideal the error wont matter. (as in salinity of 1.0159 or 1.0157 still means dead coral, but 1.026 or 1.028 could be an issue.)

Remember, arguing with an engineer is like wresting a pig in mud. Eventually you realize they like it!

:up:

Well said. I'm buying calibration fluid. Never considered this b4 as I always zeroed against ro/di...

 

[schwaggs]

EnderG60;1104796 wrote: I actually tested that. I got a bottle of fluid from BRS many years ago and have used maybe 1/4 of it and left the top off a few times, so I got another one a few months ago. Both still read exactly the same.

I calibrate mine every time I use it. Its usually only off if the temp has changed a bunch or I dropped the refectometer.

The bottles are like $8 and last forever. Just buy one for yourself. If you think its off, get another one. $8 isnt gonna break the bank.

I agree with most of what you said, however, just because your old bottle of fluid didn't drift doesn't mean everyone should keep using the same bottle of calibration fluid for years. This part of your advice is way off.

 

[civics14]

EnderG60;1104807 wrote: And that is exactly the kind of nonsense people keep saying that causes problems.

Calibration has one meaning. It means to set a standard scale of measurement. Zeroing out, is setting your range of measurements.

Think about it this way. Take your car speedometer. They are all calibrated at 35-45 mph because thats the speed you are usually at. Take into account different wheel sizes and other aspects that vary, your speedo could measure 1 mph as 0.9 or 1.1. 2 could then be 1.8 or 2.2. They can perfectly accurate at 40 but be off as much as 5 mph past 80 mph like mine is. If you calibrated at 0 mph by the time you hit 70 it would be off by 10 mph. (pulling numbers out my butt but you get the point)

If you calibrate to zero the inherent error will build up making your measurement less accurate. If you calibrate to the range your testing that error is pushed to numbers that are so far out of ideal the error wont matter. (as in salinity of 1.0159 or 1.0157 still means dead coral, but 1.026 or 1.028 could be an issue.)

Remember, arguing with an engineer is like wresting a pig in mud. Eventually you realize they like it!

So, if you calibrated it at 35-45 mph and came to a stop and the speedometer shows you're at 5mph, are you moving or stopped?

 

[enderg60]

Schwaggs;1104839 wrote: I agree with most of what you said, however, just because your old bottle of fluid didn't drift doesn't mean everyone should keep using the same bottle of calibration fluid for years. This part of your advice is way off.

Touche' and agreed.

civics14;1104857 wrote: So, if you calibrated it at 35-45 mph and came to a stop and the speedometer shows you're at 5mph, are you moving or stopped?

While its just an example....it wont show 5 mph at zero because zero is always zero. Its a multiply by zero thing. But my speedo, and pretty much everyones, are HORRIBLY inaccurate at anything under 15 mph. No one notices because no one can judge speeds that slow, no speed sings will register that low and no one cares about an exact measurement when youre driving that slow. Not noticing an inaccuracy doesnt mean its not there.

Figured all that out while "testing" the 0-60 times of different cars and realizing that 60 on the speedo could be anywhere from 55 to 70 from car to car. Also for higher numbers by getting many speeding tickets and wondering why the officer always said a different number than I was going which was usually 5-10 less than my speedo said.

 

[civics14]

EnderG60;1104925 wrote: Touche' and agreed.



While its just an example....it wont show 5 mph at zero because zero is always zero. Its a multiply by zero thing. But my speedo, and pretty much everyones, are HORRIBLY inaccurate at anything under 15 mph. No one notices because no one can judge speeds that slow, no speed sings will register that low and no one cares about an exact measurement when youre driving that slow. Not noticing an inaccuracy doesnt mean its not there.

Figured all that out while "testing" the 0-60 times of different cars and realizing that 60 on the speedo could be anywhere from 55 to 70 from car to car. Also for higher numbers by getting many speeding tickets and wondering why the officer always said a different number than I was going which was usually 5-10 less than my speedo said.

Maybe different size tires than the car was originally calibrates to? Tires not inflated properly?

 

[wade]

Just to jump in here...

You cannot calibrate anything that measures on a continual scale (eg, 0-1.04+) with a single point and be accurate. To truly calibrate, you have to know the line that it draws is consistent over its range.

What is happening with refractometers is the same thing as with your bathroom scale when you tare it. You set a 0 point (note: that could be 0 or it could be the high end, little difference) and _hope_ that your scale is accurate as you go up. True calibration should be done with no less than 3 points, but, as with a pH probe, can be done with 2. However, we cannot adjust refractometers to anything other than a single point so the reliability of the device is wholly determined by the manufacture of said device.

In the end, I would prefer to set my value at that single point closest to what I want to measure. That way you have less compensation missed nearer that point and more (up OR down) as you move away from that point.

 

[lmm1967]

wade;1104950 wrote: Just to jump in here...

You cannot calibrate anything that measures on a continual scale (eg, 0-1.04+) with a single point and be accurate. To truly calibrate, you have to know the line that it draws is consistent over its range.

What is happening with refractometers is the same thing as with your bathroom scale when you tare it. You set a 0 point (note: that could be 0 or it could be the high end, little difference) and _hope_ that your scale is accurate as you go up. True calibration should be done with no less than 3 points, but, as with a pH probe, can be done with 2. However, we cannot adjust refractometers to anything other than a single point so the reliability of the device is wholly determined by the manufacture of said device.

In the end, I would prefer to set my value at that single point closest to what I want to measure. That way you have less compensation missed nearer that point and more (up OR down) as you move away from that point.

This is why, for the most part, I see it as a tool to make sure my new water measures the same as what is in the tank when I do a water change - not really chasing a specific number so much as checking for stability.


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