Upcoming article: DIY pH buffers

[Randy Holmes-Farley]

I understand the study is old and likely irrelevant for many of the brands; time has changed.

I’m just curious why they were left out at the time of publication. Did they leave threats like (Seachem?) did to you?

I did not want to fight with companies, correct. Since I did not test all companies available, it also doesn’t suggest that those not mentioned are good. In fact, most of those available from Amazon now were either not available then, or just aren’t available to me.

 

[Miami Reef]

@Randy Holmes-Farley


I made 0.2M NaHCO3 and 1M NaCO3 solutions.


Trial 1:

I calibrated my pH probe with fresh 7 & 10 Milwaukee packets.


I used 0.2 NaHCO3 as the base and slowly added the 1M NaCO3 solution until it reached pH 10.


I required 785mL of 1M NaCO3 to achieve pH 10 in Trial 1.


Trial 2:


I calibrated my pH probe again with Milwaukee packets and made the exact stock solutions (0.2M NaHCO3 and 1M NaCO3)


I could estimate how much was needed this time, so I added the carbonate solution faster. I also didn’t magnetically stir as aggressively.


Trial 2 required 600mL of NaCO3 to achieve 10 pH.


Why did the two trials differ in the amount of carbonate added? In the first trial, I took my time adding the carbonate to avoid overshooting it. Additionally, the magnetic stirrer in trial 1 caused more surface agitation.



Curiously, when later comparing of the pH solutions from both trials, they each read 10, despite the solutions requiring different volumes of carbonate.


Happy reefing!

 

[Miami Reef]

Can you use the Henderson-Hasselbalch equation to create pH recipes?

 

[Randy Holmes-Farley]

Yes, that is exactly how to do it.

I cannot be sure why you observed what you did, but it is consistent with CO2 entering during the stirring, lowering the pH and causing the need for more carbonate.

Either way, the buffer would still be suitable, just more bicarbonate and carbonate in the first case.

You could also try adding those total amounts (either the levels you determined or the amount you calculate from the equation) without much stirring at all and see how it differs. One could even just start with carbonate and stir until the pH drops to the target.

If you try to mix a buffer by the equation alone, mix the liquids with no stirring, then shake it up just a little inside a closed bottle.

 

[Miami Reef]

The 0.2M bicarbonate solution is around 8.1 pH each time I made it. I’ll have to check again to be sure, but why can’t we use the 0.2M bicarbonate solution to check the probes accuracy?

 

[Miami Reef]

I’d eventually like to come to a place where I can add bicarbonate and carbonate solids and fill the remaining volume with water. It will be less exposed to CO2 and I think will be more consistent for others to replicate.

 

[Randy Holmes-Farley]

The 0.2M bicarbonate solution is around 8.1 pH each time I made it. I’ll have to check again to be sure, but why can’t we use the 0.2M bicarbonate solution to check the probes accuracy?

It’s just not buffered as well as a true buffer, so is more susceptible to issues such as CO2 or impurities getting into it.

 

[Randy Holmes-Farley]

I’d eventually like to come to a place where I can add bicarbonate and carbonate solids and fill the remaining volume with water. It will be less exposed to CO2 and I think will be more consistent for others to replicate.

Yes, and that is almost certainly how companies make them.

 

[Miami Reef]

If you try to mix a buffer by the equation alone, mix the liquids with no stirring, then shake it up just a little inside a closed bottle.

I did the equation and will attempt it tonight to see if the theory matches reality.

 

[Randy Holmes-Farley]

I did the equation and will attempt it tonight to see if the theory matches reality.

Sounds good!

 

[Miami Reef]

@Randy Holmes-Farley

How effective is tank water at buffering pH? Imagine calibrating a pH probe and then bottling and labeling the pH at time of collecting a tank water sample.

It could help to know when the pH probe is drifting and knowing when to recalibrate it.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley

How effective is tank water at buffering pH? Imagine calibrating a pH probe and then bottling and labeling the pH at time of collecting a tank water sample.

It could help to know when the pH probe is drifting and knowing when to recalibrate it.

It’s fairly good at some pH values and not at others. It peaks in capacity near 8.9 and an even bigger peak down in the 6’s.

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