Lesson learned about using R/O for refractometer calibration

[jason2459]

Consistency is key. If you have established a resonable calibration protocol and fairly accurate method to determin salinity and stick with it you will be fine. If you believe you are reading 34-35ppt and maintain that level you should be just fine.

Corals can be found at various salinity levels. Salinity levels can change seasonally to daily. 35ppt is the canonical surface level average and a good number to set as the baseline to measure for. If you are not precisely there you should still be just fine.

 

[jason2459]

And Randy is much better with words then I am. A quote from a recent post from him from the thread I just linked to a couple posts back.

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.

 

[Anirban]

It will be close but not exact. Also, calibration solution bought may also not be exact. You can make up your own but it also depends on you and your equipments accuracy so may not be exact. There's always a +/- varrience.

And sometimes its beyond that varience.
http://reef2reef.com/threads/does-your-calibration-solution-need-calibrated.250133/

Yes whatever we measure are actually relative. Its relative to whatever means you used to calibrate your machine. When you calibrate your refractometer with calibration buffer your plain RO/DI will read negative as the specific gravity of water the company used to make the buffer is not same as your RO/DI water. So if you can get a calibration buffer of 1.026 and calibration buffer of 0 from same company then only in that case the calibration with one should give ideal reading for another.

In case of ph meter calibration when you calibrate with ph 10 and then introduce pH 7 from same batch you will see the reading is almost at pH 7 . But if you use a pH 10 and pH 7 from different batch but same company you will still see a variation. These things happen because its hard to really control all these so minutely. These are all relative so just stick to one of the calibration method and keep salinity steady at that level.

 

[Kaba]

What do you mean you use RODI water then use calibration fluid? If I have to adjust it when I use the calibration fluid what was the reason to use RODI water?

I basically use rodi as the first point in a 2 point calibration. But just because 0 is 0 does not mean 35 is 35. I could totally just use 35ppt and call it a day, but I always rinse it off with rodi anyway, so why not check while I'm there.

 

[Kaba]

I have one of those Milwaukee things. I didn't like how you can't calibrate it... Basically makes it useless. I change 10 gallons a week and use 5 gallons of rodi ever week. Like clockwork. Using the Milwaukee my salinity was anywhere between 33 and 37ppt. If I started at 35ppt letting 5 gallons evaporate would be me at 38ppt. So I got a refractometer and some 53ms calibration fluid I stole from work. I'd 0 the Milwaukee and read the calibration fluid, a day I'd get 33 to 37ppt. Refractometer holds calibration like a champ. I check it every time but never need to change anything.
Then I take a gallon to work and throw a YSI 6600 in there and get 35ppt like my refractometer says.

 

[reeferfoxx]

I have one of those Milwaukee things. I didn't like how you can't calibrate it... Basically makes it useless.

WHAT!?
Explain how or where it says you cannot calibrate it? The calibrate button is on the unit itself! It says "Zero". You add distilled water and press the 'Zero' button and.. done.........

 

[stunreefer Verified Sponsor]

i use ro to calibrate

i think refractometers that are dropped or damaged use the fluid to offset their cheaply made/damaged devices.

think about it...

you just calibrated to 1.026 using 1.026 fluid and register negative numbers with ro.

the device is shot

False.

This device has a very large scale, and by calibrating with RO/DI you have assured the lowest reading will be accurate, but not mid-range (which we care about) or high range. As stated previously most hobby refractometers only have one calibration point rather than several. So we calibrate to the point closest to our use.

 

[Kaba]

That's not a calibration, that's a zero. A calibration would be like for a pH probe, we put the probe in a solution of known pH and tell the meter "ok, this is what pH 7 is." You can't do that with a Milwaukee. You can only tell it was 0 is and hope for the best. But since we're well above 0 it's practically useless. It's been said before (by me and others) but when we calibrate our pH probes, we use 2 solutions, usually 7 and 10. We dip the probe in 7 and tell the meter this is 7, then rinse it off and dip it in 10, and tell it that is 10. That is a simple 2 point calibration. Anything less isn't a calibration. Using rodi would be a blank, and using 35ppt to make sure it's reading 35ppt would be a check standard.

 

[reeferfoxx]

That's not a calibration, that's a zero. A calibration would be like for a pH probe, we put the probe in a solution of known pH and tell the meter "ok, this is what pH 7 is."

Seriously? So the 35ppt solution that comes with the milwuakee meter is just for looks and has nothing to do with the accuracy of the meter? That 'Zero', is to calibrate the meter at zero for zero salinity solution. Your statement is absurd.

 

[Kaba]

Seriously? So the 35ppt solution that comes with the milwuakee meter is just for looks and has nothing to do with the accuracy of the meter? That 'Zero', is to calibrate the meter at zero for zero salinity solution. Your statement is absurd.

You can use it to check your meter, but if all of a sudden 35 no longer reads 35 (like in my case) what do you do?
The zero on the meter is useless. You're never going to need to read 0ppt. It would be better if that was a 35ppt button, at least then you can tell the meter the 35ppt standard you put on there is reading properly.
My day job is analyzing organic pesticides through gc/ms, I know a thing or two about calibration, and the Milwaukee can't do it.
Next time you need to calibrate your pH probe use a 2 and 4 solution and let me know how that works our for you.

 

[reeferfoxx]

Then why are you comparing apples to oranges? You are comparing conductivity probes to light refraction. If you are dipping a probe in 7ph solution and telling the probe what 7pH is, then telling a light refractor what 0 salinity is the exact same thing.

 

[Kaba]

Then why are you comparing apples to oranges? You are comparing conductivity probes to light refraction. If you are dipping a probe in 7ph solution and telling the probe what 7pH is, then telling a light refractor what 0 salinity is the exact same thing.

No, it's not. When you calibrate a pH probe with 2 solutions, it is building a calibration curve to relate your new unknown pH to in order to give you a proper pH value.
The point you aren't getting is that you don't want to read your tank at 0ppt, so calibrating it with 0ppt water is useless. It would be like calibrating a balance with a 1 gram standard weight, then weighing a bushel of apples. You're now so far away from where you calibrated, that calibration is useless.
It doesn't matter if the meter reads volts, fluorescence, light absorbance, conductivity, or resistance, a calibration is still a calibration. And the Milwaukee doesn't do it. Using rodi on a refractometer doesn't do it either.

 

[reeferfoxx]

I guess it doesnt make sense to me that you think the calibration should be close to the specific gravity you are trying to get. Or that that is even logical. You would think that if a meter can differ from 0.000 SG and 1.026 SG that that would be a good thing. But i guess if my refractometer can give those two readings and be accurate at it, that it must be trash?

 

[Kaba]

It's not that I think that's how it should be, that's what a calibration is. You can't properly calibrate with 1 point, and calibrating far from your target is useless. If I'm running a sample at work and one of my target pesticides is at 1005ppb, and my highest standards is 1000...that sample has to be diluted to read within the calibration curve.
Why do you care what 0ppt is when you need to measure 35ppt? What do I do with my Milwaukee? I zero it with rodi and then my 35ppt standard is anywhere between 33ppt and 37ppt. How do I know what is right?
If your refractometer can read 0 and 35ppt accurately then great, so can mine. But if you calibrate to 0 and then a 35ppt standard comes out at 34, what do you do? Is the refractometer off at 35ppt or is it off at 0?

 

[reeferfoxx]

But if you calibrate to 0 and then a 35ppt standard comes out at 34, what do you do? Is the refractometer off at 35ppt or is it off at 0?

I would declare the refractometer to be junk at that point. My point is, mine reads accurately but you are telling me it doesn't and that all milwuakee meters are useless.. LOL If you "calibrate" it at 0ppt and the 35ppt solution reads 35ppt then all is well. But yes, if I zero'd my calibration and got a reading of 34ppt then I call about my warranty.

I'm a Digital intermediate colorist and when I "calibrate" my monitor for 6000k SRGB or Adobe I rely on a colorimeter that may or may not be calibrated to factory standards then I have a problem and I call the manufacturer.

All you are doing is write a long statement about how things break. Because, your fancy meters might not calibrate correctly at some point too.

 

[Kaba]

I'm not telling you that at all. I'm saying using rodi water is pointless.
If you calibrate your monitor to 6000k, why not try 3500k? Or 8000k? You wouldn't calibrate your monitor to something you don't need. Same thing with a refractometer. I'm not measuring 0ppt in my tank, so it's ability to measure 0ppt is moot.

 

[reeferfoxx]

Well SRGB is 6000k and Adobe is 5000k. I have to switch frequently depending on the application(IE TV, internet, tablet, cell phone, photographic paper, etc etc) But anyway. I agree that measuring for 0ppt is moot but i don't agree with you that setting the calibration at 0ppt is moot. Hasn't ever effected my tank. I like knowing that my refractometer can tell the difference between 0ppt and 35ppt without any issues. As crappy as that may sound...

 

[redfishbluefish]

Maybe I can explain the RO/DI standard specifically for the Milwaukee Digital Refractometer. This guy works differently when compared to the hand-held "spy glass" refractometer we are use to. The Milwaukee uses a specific wavelength of light and actually measures the Refractive Index. It then does the math to convert it to three different user picked choices. It needs to be "zero'ed" to determine the angle of refraction. I believe it would be consider a pure number. So you need to use pure water to determine a starting point (zero the unit). I hope that's a clear explanation.

And therefore, @reeferfoxx , I speculate that you have a bad meter or bad calibration fluid if you're not getting 1.026 SG when reading this fluid.

 

[reeferfoxx]

And therefore, @reeferfoxx , I speculate that you have a bad meter or bad calibration fluid if your not getting 1.026 SG when reading this fluid.

I didn't start the OP. This thread belongs to someone else. My meter reads just fine. Kaba is just tell me how all milwuakees are broken.

 

[redfishbluefish]

I didn't start the OP. This thread belongs to someone else. My meter reads just fine. Kaba is just tell me how all milwuakees are broken.

Oops! I'm sorry, with your banter back and forth, I confused the two of you....so @Kaba , has the unit that is not reading calibration fluid correctly. Sorry! Either a bad meter or bad calibration fluid.