Upcoming article: DIY pH buffers

[Randy Holmes-Farley]

pH buffers are very simple to make, and are surprisingly expensive to buy. For that reason, I thought DIY pH buffers would be a good article in the future. Easy to make, last a good while in a cheap closed soda bottle, and one can easily make a lot at once.

What I don't know is what pH values people really need these days. Obviously we want to bracket the pH in reef tank, with something like 7 and 10.

Many pH meters allow you to use most any pH values you want to calibrate, and can use more than 2 buffers.

But the simpler devices are usually only 2 (just one is a bad idea), and often they are fixed.

So what fixed values do people need?

One reason I'm asking is that a surprisingly large numbers of inexpensive buffer packet sets are 4, 7, and 9.18. I've never personally used a meter that needed pH 9.18, but they may exist.

Are there common reefing pH meters that need pH 9.18 for calibration? If so, its easy to make. if not, I won't bother since some do require pH 10.

TIA.

 

[Miami Reef]

I think most pH probes specifically require 7 and 10 solutions.


Apex and Hanna, for example, do not allow you to input specific calibration values; you can choose 4, 7, or 10.


I’m very excited! Highly accurate DIY pH solutions would change reefing!

 

[Garf]

An 8.2 would be good, even if just a reference to allow users to mentally adjust the current calibration. Borax is good but still a way off from what we have our tanks at. I'm just off to buy shares in a magnetic stirrer company.

 

[Randy Holmes-Farley]

I won't be testing and posting recipes for a while, but for folks who want to mess around, there will be two ways to do it. The old standby science way involving mixing two exactly known solutions in a known ratio.

or

The new RpB method (Randy pH Buffer) lol

Buy 2 buffer packets (or bottles), pH 7 and 10, and carefully calibrate your meter.

For any pH desired from 9.2 to 10.6. Best buffering at ~ pH 10. Start with 0.2 M sodium bicarbonate (16.8 g/L, exact value not critical) and slowly add sodium carbonate to it (could be dry solids or a solution of similar strength) until the pH reaches pH 10 (or whatever buffer pH is desired). Done, Bottle it up and enjoy.

For any pH desired from 5.8 to 8.0 (so could be 7 or 8, but pH 8 is much weaker buffering). Start with 0.2 M sodium phosphate dibasic (Na2HPO4; 28 g/L) and slowly add sodium phosphate monobasic to it (NaH2PO4could be dry solids or a solution of similar strength) until the pH reaches pH 7 (or whatever buffer pH is desired). Done, Bottle it up and enjoy.

I'll have to work up a good recipe for 8.2, but a borax/phosphate mix would likely be better than the 8 end of the phosphate buffer above.

The old fashioned science way is here, with detailed recipes. The problem is knowing exactly how much moisture is in the solids you use. Chemists will buy or make carefully known solids to do this, but reefers can use the RpB way and not worry about such issues since the use a a pH meter eliminates concerns.

https://www.promega.com/resources/guides/lab-equipment-and-supplies/buffers-for-biochemical-reactions/#:~:text=Preparation%20of%20Phosphate%20Buffer%20(pH,8.0%20at%2025%C2%B0C)&text=Phosphate%20Buffer.

 

[Miami Reef]

I think I like the old-fashioned science better.

Using the RpB Method has two downfalls, in my current opinion:

1) It requires buying 7 & 10 solutions, which is a catch-22.

2) It involves trusting those pH packets and their companies. It would be ironic if you made new standards with a solution you don’t trust; if the initial standard isn’t trustworthy, future standards with that calibrated probe would also be untrustworthy.

 

[Garf]

It involves trusting those pH packets and their companies.

I too do not trust those cheap packets.

 

[EricR]

2) It involves trusting those pH packets and their companies. It would be ironic if you made new standards with a solution you don’t trust; if the initial standard isn’t trustworthy, future standards with that calibrated probe would also be untrustworthy.

Yeah,,, I kinda wonder about the accuracy of the mass produced standards almost as much as the accuracy of the meter itself.

Mine (handheld) allows up to 5-point calibration (1.68, 4.00, 7.00, 10.01, 12.46),,, but I only ever do 7 and 10.

 

[Garf]

Hold me back from posting this link on the Bolus thread. No, I mean it, stop me.

 

[Garf]

Too late

 

[Pod_01]

So GHL KH Director uses pH 4 calibration fluid. Can that be added?

 

[A_Blind_Reefer]

I won't be testing and posting recipes for a while, but for folks who want to mess around, there will be two ways to do it. The old standby science way involving mixing two exactly known solutions in a known ratio.

or

The new RpB method (Randy pH Buffer) lol

Buy 2 buffer packets (or bottles), pH 7 and 10, and carefully calibrate your meter.

For any pH desired from 9.2 to 10.6. Best buffering at ~ pH 10. Start with 0.2 M sodium bicarbonate (16.8 g/L, exact value not critical) and slowly add sodium carbonate to it (could be dry solids or a solution of similar strength) until the pH reaches pH 10 (or whatever buffer pH is desired). Done, Bottle it up and enjoy.

For any pH desired from 5.8 to 8.0 (so could be 7 or 8, but pH 8 is much weaker buffering). Start with 0.2 M sodium phosphate dibasic (Na2HPO4; 28 g/L) and slowly add sodium phosphate monobasic to it (NaH2PO4could be dry solids or a solution of similar strength) until the pH reaches pH 7 (or whatever buffer pH is desired). Done, Bottle it up and enjoy.

I'll have to work up a good recipe for 8.2, but a borax/phosphate mix would likely be better than the 8 end of the phosphate buffer above.

The old fashioned science way is here, with detailed recipes. The problem is knowing exactly how much moisture is in the solids you use. Chemists will buy or make carefully known solids to do this, but reefers can use the RpB way and not worry about such issues since the use a a pH meter eliminates concerns.

https://www.promega.com/resources/guides/lab-equipment-and-supplies/buffers-for-biochemical-reactions/#:~:text=Preparation%20of%20Phosphate%20Buffer%20(pH,8.0%20at%2025%C2%B0C)&text=Phosphate%20Buffer.

Are you now coining “old fashioned science way”? I think that’s already been taken…..

 

[A_Blind_Reefer]

Hold me back from posting this link on the Bolus thread. No, I mean it, stop me.

I saw that….I was going to ask if that was a non-subliminal, subliminal message ha

 

[Garf]

I saw that….I was going to ask if that was a non-subliminal, subliminal message ha

Lol. I'm guessing some magical effects with regard to pH will be squashed with a reliable pH reference solution.

 

[ingchr1]

Would these be more trustworthy than the packets?

Amazon product

 

[areefer01]

Apex and Hanna, for example, do not allow you to input specific calibration values; you can choose 4, 7, or 10.

I can't speak for Hanna but with regards to Apex there are two options within the ph calibration task.

• Low 4.00, high 7.0. They note Fresh Water, Calcium Reactor use case.
• Low 7.00, high 10.00 Salt Water.

I thought back in the early days they allowed us to enter the number but maybe that was changed a while back /shrug

 

[Randy Holmes-Farley]

I think I like the old-fashioned science better.

Using the RpB Method has two downfalls, in my current opinion:

1) It requires buying 7 & 10 solutions, which is a catch-22.

2) It involves trusting those pH packets and their companies. It would be ironic if you made new standards with a solution you don’t trust; if the initial standard isn’t trustworthy, future standards with that calibrated probe would also be untrustworthy.

I would note that most chemistry labs are very unlikely to make pH standards from dry chemicals . They buy them and use them, and you can buy NIST traceable standards. I’m not suggesting that folks buy the cheapest standards possible to use as an RpB standard. That said, the article will have dry chemical recipes too.

https://www.coleparmer.com/p/oakton-traceable-ph-buffer-solutions/59252

OAKTON
NIST-traceable reference materials include a calibration report from an ISO 17034 and ISO 17025 accredited laboratory

• Choose from clear or color-coded standards from common calibration points

Oakton pH buffers are compared against, and are traceable to, NIST Standard Reference Materials. Each bottle includes a NIST-traceable calibration report stating accuracy at 25°C to ±0.010 pH. Color-coded and colorless buffers are available in 500-mL, 1-L, or 4-L packaging sizes. Additional values and packaging sizes are available. Store at room temperature.

 

[Randy Holmes-Farley]

I saw that….I was going to ask if that was a non-subliminal, subliminal message ha

How would one know? lol

 

[A_Blind_Reefer]

Out of curiosity…..who was the anti-ocd, madman that came up with 10.01 as a buffer? I’d give them credit if they were dyslexic I guess. It’s just cringe for me….Not that it makes a difference one way or the other but at least give me that option on the device. Ha

 

[Miami Reef]

I would note that most chemistry labs are very unlikely to make pH standards from dry chemicals . They buy them and use them, and you can buy NIST traceable standards. I’m not suggesting that folks buy the cheapest standards possible to use as an RpB standard. That said, the article will have dry chemical recipes too.

Is it a correct assertion that making an RpH standard will only be as accurate as the initial standard used to calibrate the probe?

 

[Randy Holmes-Farley]

Is it a correct assertion that making an RpH standard will only be as accurate as the initial standard used to calibrate the probe?

Yes, that is correct.

So one can use it two ways (or something in between):

1. Use whatever standard you have been, and make more calibration standard fluid at close to its accuracy, whatever it is, at a much reduced cost.

or

2. Use a very high quality standard, such as the ones I linked, and then have inexpensive secondary standards that are close, but obviously not quite as accurate.

My recommendation in either case is to make multiple bottles of standards at once and seal them up and use them for a long time with some bottles maybe not opened for a year or more before first use, rather than repeatedly making new standards off the old standards. The standards will certainly drift over time with each generation.

In the past, this is what I actually did:

1. I had multiple 500 mL bottles of expired standards my old lab got rid of.

2. Every once in a while, I'd get new packets of pH standard, calibrate, then measure all of those old bottles for ph, and I relabeled them to the new level. Some had many pH revisions written on them, along with a date, and the higher pH fluids would tend to drift down over time. Since my pH meter allowed any value for calibration, the pH 10 ones, for example, were entered during calibration as 9.92 or 9.86 or whatever they might actually be.