Warning: Commercial pH Calibration Buffers can be way off!

[Randy Holmes-Farley]

pH problems are among the most common problems in the Reef Chemistry forum here at RC. While I expect the vast majority of these problems are real, pH calibration is also a substantial issue.

A while back it was suggested to me that there may be a problem with certain commercial pH calibration buffers used by aquarists. So I set out to test a bunch by buying a variety of different brands and pHs from a variety of popular online vendors and an LFS. Some were intentionally expired, to see the effects of aging. I will report in detail on these tests next month in an article at reefkeeping.com

Frankly, however, I was shocked by the results, and feel the urgency to release some information right away.

One brand was so seriously in error that it could cause serious problems should aquarists use them and accept the results.

I'm not talking about small differences that only chemists or perfectionists would care about. I'm talking about a pH 4 buffer over pH 6, several pH 10 buffers from a single brand at pH 9.0, a pH 7 buffer at pH 7.5. These are serious errors.

I have reluctantly decided to not name the particular brands that performed poorly (even by email or PM, so please don't ask).

Instead, I will provide the list of brands below that indicate those brands that seem sufficiently accurate to me for reef aquarists to get useful results (although that does not imply that all samples from each listed brand were perfect):

Orion PerpHect packets
Milwaukee packets
Pinpoint packets
Hanna bottles and packets

So my recommendation is to use one of these brands, unless you have good reason to trust another brand.

Happy Reefing.

[jfinch]

Wow! I'd have never thought that to be a problem. It's not like making up a buffered solution is rocket science.

I'm not sure if you can or will answer this, but did you check any buffers from Ricca Chemical http://www.riccachemical.com/

How did you know your pH meter was properly calibrated (what brand buffer did you use or did you use some other method of calibration).

[Randy Holmes-Farley]

Sorry, if I answer which ones that I did not test, folks will quickly conclude which ones that I found bad.

How did you know your pH meter was properly calibrated (what brand buffer did you use or did you use some other method of calibration).

That's a good question. I used new packets of pH 7 and 10 calibration buffers from Orion. I tested several packets from them, and a number of other manufacturers (those listed above). All were close enough to conclude that those that were off were outside of the envelope of reproducibility. There were, for example, about 17 different pH 10 buffers with a value between 9.90 and 10.04. None of the samples of what I consider lab brands mentioned above were outside this range. I wouldn't try to make a point of 0.1 pH units. But the 3 samples from a single brand of pH 10 buffer that came out between 9.01 and 9.03 are clearly a problem (IMO).

[jfinch]

Sorry, if I answer which ones that I did not test, folks will quickly conclude which ones that I found bad.

:lol: didn't take the bait, eh? Maybe you are smarter then the average dog :D

Thanks for the other info!

[Ron83]

Randy, Is Milwaukee Liquid bottles the same as Milwaukee Packets?

If not, didn't you also do an article on a Homemade pH Calibration solution. Tried to search for it but search was down again. If so can you provide the link.

Thanks

[Boomer]

Milwaukee packets Pinpoint packets Hanna bottles and packets

I never would have guessed that:rolleyes:

didn't take the bait, eh?

You need a bigger minnow :D




Ron


He never did one on pH calibration solutions, it was for salinity

[Ron83]

Ron,
Yah, Just found it and thought it was Randy but someone else.

Not to "wreck" the article, but do you see anything wrong with using this to check to see how our close our PH monitors are with the solutions we are using to adjust them.

----------------------------
1/2 Teaspoon "20 Mule team borax to 1 pint distilled water (3.8 grams per liter) PH is temp. dependent -see article

http://web.archive.org/web/20010721095642/fpage1.ba.best.com/~cbingman/
---------------------------

Or did someone buy stock in the above listed solutions before the big run-up :mixed: :rollface:
Just kidding!

[Randy Holmes-Farley]

That is a fine article and a fine way to verify pH readings. :). I linked it in the duplicate thread to this one in the main forum, and will link it in the article that I write. :)

[Randy Holmes-Farley]

Randy, Is Milwaukee Liquid bottles the same as Milwaukee Packets?

I'll look back at my notes later (actually, my 7 year old daughter, Savannah, took the notes :D ), but it was probably only packets that I tested from Milwaukee.

[Randy Holmes-Farley]

didn't take the bait, eh? Maybe you are smarter then the average dog

Definitely smarter than our last Golden Retriever. :D

Milwaukee packets Pinpoint packets Hanna bottles and packets

I never would have guessed that


:lol:

[Ron83]

Ok, I just took the Boarx challenge.

Tested my solutions, 7.01 & 10.01 , and some fresh made borax/distilled water with my checker by Hanna.
Everything was high to +.10 after compensating for temperature.

Since my checker is only accurate to +-.2 I think I am safe and will just remember my Checker is .1 high until next time I adjust it.

Also, isn't distilled water supposed to have a PH of 7.0 - would this work for people without access to borax or does it vary by brand?

[Randy Holmes-Farley]

No, distilled water pH is not suitable. Meters and kits do not accurately read the pH of purified water, and carbon dioxide enters it from the air, dropping the real pH to between 5.5 and 7.

FWIW, my purified RO/DI water reads above ph 9. I do not know if that is real or not.

Since my checker is only accurate to +-.2 I think I am safe

I'm glad it checked out. :)

[spyro]

I have always used the Hach "pillows" which are sealed plastic containers of powder to make 50 ml of calibration fluid. I use the
pH 10 and the pH 4 solutions that are supposed to be accurate to pH = 10 +/- .02, and pH = 4 +/- .02 at 25 degrees C or about 75 degrees F.

Randy, did you test this brand ?

[Randy Holmes-Farley]

As I mentioned to Jon, I can't really mention whether I tested particular brands or not, without revealing the brands that I found troubles with. Sorry.

I can say, however, that there are lots of brands that one can buy. More than I tested.

[mattseattle]

Pinpoint packets

is this the American Marine product ?

[jfinch]

As I mentioned to Jon...

Strike two...

[Boomer]

Pinpoint packets

is this the American Marine product ?

Yes :D That is not an issue Matt

American Marine is the name of the company and Pinpoint is the name of their product line

Home run Jon :lol:

[Randy Holmes-Farley]

Randy, Is Milwaukee Liquid bottles the same as Milwaukee Packets?

The Milwaukee bottles that I tested were OK. :)

[mattseattle]

thanks everyone!

[marm64]

Wow here you think that you are having trouble with your pH meter and in therory it could be your pH calibration buffers.

Thanks Randy

[Randy Holmes-Farley]

Yes, it was a surprising result for me. :(

[loudell]

Garbage in....garbage out

[a4]

Garbage in Garbage out. Funny, I know the company that made junk buffer.

They don't advertise here anymore. The pH monitor made by them are junk too.

[NicoleC]

Interesting. I have some of the whitelisted calibration packets above. but I am starting to think my pH readings are still junk. My meter is also made by one of those companies with good calibration fluids, but that may not mean anything. May I suggest a followup study on hobby-level pH meters themselves?

[loudell]

Generally, ph equipment is linear electronic equipment which verifies that it is working when a sucessful calibration is carried out. Why do you feel that your pH readings are "junk"?

[NicoleC]

My pH seems unreasonably low given the other conditions in the tank. Even using the aeration test, the pH will not rise above 8.1 -- or rather, won't test above 8.1. I've been driving myself nuts with chemistry experiments.

A friend thought his pH meter was off because his readings were too high and was dosing vinegar, so I brought mine over. His unit's reading was 8.7 -- mine was 1.6! Both units had just been calibrated. Clearly, one unit was not giving a correct reading. I suspect both units are giving false readings.

[loudell]

Electronic pH should be a definitive and unemotional test.
1-Calibrate the meter using accurate fluids.
2-measure the tank water
3-go back to the calibration fluids to see if the calibtation has drifted

There may be a few isolated phenomena but generally not...

[Randy Holmes-Farley]

If you suspect that your pH meter may be off, despite proper calibration, you can always test it in borax/water:

Borax pH Verification
http://web.archive.org/web/20021015005420/www.animalnetwork.com/fish2/aqfm/2000/feb/bio/default.asp

[Hobster]

Ok what do I believe? I suspected my pH pen was off so I calibrated this weekend using Pinpoint packets of 7 and 10. The 7 was off on my pen the 10 was dead on. I then did the Borax and only got 9.0 not 9.2. (1/2 tsp in 16oz ro/di) I would imagine the pH packets would be more accuarate?

[Randy Holmes-Farley]

I calibrated this weekend using Pinpoint packets of 7 and 10. The 7 was off on my pen the 10 was dead on.

So you reset them and the 7 and 10 both read correctly after calibration? The packets were freshly opened?

[loudell]

The 7 was off on my pen the 10 was dead on

Mmmmm. a pen. Is it a 2 point calibration instrument?
When you say the 7 was "way off"; what is way off to you?

[Hobster]

Originally posted by Randy Holmes-Farley
I calibrated this weekend using Pinpoint packets of 7 and 10. The 7 was off on my pen the 10 was dead on.

So you reset them and the 7 and 10 both read correctly after calibration? The packets were freshly opened?

Yes and yes. I did not adjust the 10 as it was reading 10.

The 7 read 7.4 before adjusting.

Milwalkee pen. only measures to 1 decimal place.

I compared to a Seachem pH test kit and it seems correct. As close as one can tell by color chart.

[Randy Holmes-Farley]

So the 10 still read right after adjusting the 7? One would expect the 10 to move when adjusting the 7 by 0.4 pH units.

After calibration, the pen ought to be put back in the 7 and 10 and it should be able to read both correctly at that time.

[ssheipel]

Can I ask a question here?

About tempurature and pH buffers. How do I calibrate my pH meter, taking into account the differences in pH readings various temps of the buffer will provide?

I fear it's a stupid question since the differences are marked on the side of the pinpoint packets I use to calibrate, but it's still too much for my far far far from logical/mathematical mind! :)

I don't want to hijack the thread , but it seemed like a good point in this discussion to ask.

steve

[Randy Holmes-Farley]

No, that is a good question. :)

The answer depends on your pH meter. If you can adjust the pH meter to different temperatures with a temperature setting, and can also adjust the meter to pH values such as 10.06 for the calibration, then set it to the actual temperature of the buffer and the pH that the buffer packet indicates (interpolate, if necessary, for vlaues between the packet indications).

If you cannot use values different than exactly 7 and 10, then things are a little tougher. Try to use a temperature that is close to the temp where the packets have exactly 7 and 10.

If you cannot adjust the pH meter to different temperatures, then try to calibrate near the temp that the buffers will match the meter, or if the meter is adjustable, use a temp close to the tank temperature.

There is additional info in this article:

Measuring pH with a Meter
http://www.advancedaquarist.com/issues/feb2004/chem.htm

[Hobster]

Originally posted by Randy Holmes-Farley
So the 10 still read right after adjusting the 7? One would expect the 10 to move when adjusting the 7 by 0.4 pH units.

After calibration, the pen ought to be put back in the 7 and 10 and it should be able to read both correctly at that time.

Yes, this was done several times and each time was correct.

How accurate is the Borax? Per the article it seems that small amounts + or - should not make much differance (.2)

What should the pH be of 2 tsp of lime in 1 gal. Maybe I can use that as check? (75 F)

[ssheipel]

Thanks Randy.

My pH meter (pinpoint) does not adjust for temp (unless I missed something in the instructions!! -- will have to revisit). So what I should be doing, yes?, is trying to bring the buffer solution to the tempurature where it will give the proper value (7 and 10 in this case) before calibration?

Does it then matter if the aquarium temp is different from the temp of the buffers used to achieve the calibration measurements?

In my confusion am I making sense?

Oh, and I've read the article several times :)

steve

[Randy Holmes-Farley]

It is accurate in theory, but in practice with issues like ambient CO2 entering the water or even the dry borax, I do not know for sure.

Truly saturated limewtaer (say, 2 teaspoons in a cup of purified water) has a pH of 12.454 at 25 deg C, but it does vary with temp. It may not be a good way to check a calibration or measurement at much lower pH values (like 8.2).

FWIW, did you have the buffer packets at the right temp? What about the borax solution?

To be fair, a difference of 0.2 pH units at pH 9.2 may only translate to a difference of about 0.1 pH unit at pH 8.1 (assuming the pH 7 is correct) and so may not matter much for most purposes.

To have the borax at a real 9.2 read 9.0, the pH 10 calibration buffer (if it alone was the cause) would have to be over 10. If anything, I'd expect errors on the other side (and did observe them on the low side, even for Pinpoint).

So I'd probably just split the difference, and conclude that the real pH may be a tad above what you measure. :D

[Hobster]

I did not take the temp of the test solutions or Borax. I would guess they range close to 70 to 75 degrees . Below is the pen in question, I thought with ATC, temp would not be a factor? Now that I look at the specs a little closer, if the accuracy is +/- .1 pH, then like you say it is probably as close as it will get.:)

pH51

Specifications: Range 0.0 - 14.0 pH
Resolution 0.1 pH
Accuracy ± 0.1 pH
Calibration Manual 2 points
Electrode Replacable MA73600
Battery Life 1500 hours of continuous use
Battery Type 3 x 1.5V
Environment 0 – 50°C / 100% RH

Accurate and reliable Waterproof pH/°C tester

Double junction replaceable pH glass electrode
IP67 Waterproof casing
Automatic calibration
Auto Shut-off after 8 minutes

[Randy Holmes-Farley]

Below is the pen in question, I thought with ATC, temp would not be a factor?

It is likely small, but the ATC does not take into account how the actual pH of buffers change with pH. It just adjusts for how the meter responds as a function of pH. I discuss that difference in the article above.

[alrha]

how sensitive are the packets? If you use the temp probe from the tank in the packet to verify the temp, would it contaminate/alter the pH of the calibration at all, or is that negligible?

[Randy Holmes-Farley]

The buffering capacity in such packets is typically much higher than the tank, so they are resistant to moving too much, but I'd rinse the pH and temperature probes in DI water before putting them into calibration packets.

[Hobster]

OK, last night I tried again:

2 tsp lime in 8 oz ro/di at 75-80 degress = pH of 12.1

1/2 tsp Borax in 16 oz ro/di 75- 80 = pH of 9.0

So I am thinking I either calibrated wrong, my calibration packets were off or something is just not Kosher.:)

I ordered some new fluid and will calibrate again.

This is frustrating as I have always had a low pH problem despite trying all the recomendations and to now have it read another .2 units or so low is a pain.:(

[Randy Holmes-Farley]

Let us know if anything different arises when the new packets are used. :)

[loudell]

Keep in mind that the pen accuracy is +/- .1 which is actually pretty large...