Aeration test - temperature change

[rishma]

I want to perform Randy’s often cited aeration test but I want to result to be fairly precise. It’s getting cooler outside and the outdoor aerated sample will cool down. I am thinking of ways to do the test without heating the sample while aerating.

If I put the aerated sample in sealed bag, then float it in the tank to warm warm back up before measuring pH I think this will eliminate most of the error. The only issue is CO2 is more soluble at lower temps, so the pH of the bagged water might still be lower even after I warm it up?

Temp change won’t be huge if I do it tomorrow so I understand if the answer is don’t worry about it. I am being a bit lazy and not figuring out the impact temp/CO2 solubility on pH myself. I know there is data out there.

Would appreciated some thoughts and ideas.

https://www.reefedition.com/ph-and-the-reef-aquarium

 

[rishma]

Maybe if I include a gas cap of outdoor air in the sealed bag and then float it will be closer to equilibrium when it warms up.

 

[Miami Reef]

My original question:

Question #3

Is it true that a 5C difference in temp can alter the pH probe’s reading by about 0.05 - 0.1 units, even though the actual pH hasn’t changed?

I’m assuming this effect is for pH probes without ATC.


Randy’s response to it:

I discuss temp effects on pH here:

https://reefs.com/magazine/aquarium-chemistry-measuring-ph-with-a-meter/

Temperature Effects on pH Measurement​

There are two different ways that temperature impacts pH measurement. The first involves actual chemical changes in the solution that you are measuring. Acids can, for example, become stronger or weaker as the temperature is changed. This is how calibration standards change their pH as a function of temperature (which is discussed in more detail in the calibration section below). If the solution has solids in contact with it (as is the case with saturated limewater in the presence of excess solids), the temperature can also impact how much acid or base is in solution impacting pH, and how much is just solid sitting on the bottom of the container. These effects are specific for every solution that you will encounter, and there is nothing general that one can or should do about this, except be aware that it happens.

The second impact of temperature is on the pH electrode itself. pH electrodes change their response in a very clear way as temperature is changes. They respond more strongly to pH changes at higher temperature than at lower ones. At 100 ºC, they change their output potential by 74 mV/pH unit, and at 0 ºC, they change by 54 mv/pH unit. Because pH meters are typically standardized at pH 7 (that is, zero mv = pH 7), the error from temperature differences gets greater and greater as the pH being measured gets further from 7. So it may be trivial when measuring something with a pH of 7.1, but very important when measuring something with a pH of 10 (or when calibrating with a pH 10 buffer).

There are usually three different ways of taking temperature into account. One is to make measurements close to the temperature at which you calibrated the meter (say, within a few degrees). The second is to “tell’ the meter what the temperature is (digitally or with a dial). The third is that some meters have a temperature probe, usually called an ATC, which you stick into the measuring solution. This probe reports the temperature back to the meter, and the meter makes any necessary corrections (for this type of temperature effect).

As long as you use one of these three ways of dealing with temperature issues, you will get reasonably accurate readings.

From this thread:

https://www.reef2reef.com/threads/h...e-carbonate-equilibrium.1118837/post-13704874

 

[Miami Reef]

I’m like an encyclopedia where I can remember which things people say in which threads. Ha

 

[Fish Fan]

I’m like an encyclopedia where I can remember which things people say in which threads. Ha

I've got a mind like a steel trap. Once it gets in there, it never gets out again

 

[rishma]

My original question:

Question #3

Is it true that a 5C difference in temp can alter the pH probe’s reading by about 0.05 - 0.1 units, even though the actual pH hasn’t changed?

I’m assuming this effect is for pH probes without ATC.


Randy’s response to it:

I discuss temp effects on pH here:

https://reefs.com/magazine/aquarium-chemistry-measuring-ph-with-a-meter/

Temperature Effects on pH Measurement​

There are two different ways that temperature impacts pH measurement. The first involves actual chemical changes in the solution that you are measuring. Acids can, for example, become stronger or weaker as the temperature is changed. This is how calibration standards change their pH as a function of temperature (which is discussed in more detail in the calibration section below). If the solution has solids in contact with it (as is the case with saturated limewater in the presence of excess solids), the temperature can also impact how much acid or base is in solution impacting pH, and how much is just solid sitting on the bottom of the container. These effects are specific for every solution that you will encounter, and there is nothing general that one can or should do about this, except be aware that it happens.

The second impact of temperature is on the pH electrode itself. pH electrodes change their response in a very clear way as temperature is changes. They respond more strongly to pH changes at higher temperature than at lower ones. At 100 ºC, they change their output potential by 74 mV/pH unit, and at 0 ºC, they change by 54 mv/pH unit. Because pH meters are typically standardized at pH 7 (that is, zero mv = pH 7), the error from temperature differences gets greater and greater as the pH being measured gets further from 7. So it may be trivial when measuring something with a pH of 7.1, but very important when measuring something with a pH of 10 (or when calibrating with a pH 10 buffer).

There are usually three different ways of taking temperature into account. One is to make measurements close to the temperature at which you calibrated the meter (say, within a few degrees). The second is to “tell’ the meter what the temperature is (digitally or with a dial). The third is that some meters have a temperature probe, usually called an ATC, which you stick into the measuring solution. This probe reports the temperature back to the meter, and the meter makes any necessary corrections (for this type of temperature effect).

As long as you use one of these three ways of dealing with temperature issues, you will get reasonably accurate readings.

From this thread:

https://www.reef2reef.com/threads/h...e-carbonate-equilibrium.1118837/post-13704874

Thanks. Very helpful.

I’ll make the temperatures of the samples at the time of pH measurement the same. Now to understand if the temp impact on the solubility of CO2 during the aeration step is a big enough impact to worry about. I found a couple papers about temp impact on seawater pH but they are behind the paywalls so I cannot see the data.

 

[rishma]

My original question:

Question #3

Is it true that a 5C difference in temp can alter the pH probe’s reading by about 0.05 - 0.1 units, even though the actual pH hasn’t changed?

I’m assuming this effect is for pH probes without ATC.


Randy’s response to it:

I discuss temp effects on pH here:

https://reefs.com/magazine/aquarium-chemistry-measuring-ph-with-a-meter/

Temperature Effects on pH Measurement​

There are two different ways that temperature impacts pH measurement. The first involves actual chemical changes in the solution that you are measuring. Acids can, for example, become stronger or weaker as the temperature is changed. This is how calibration standards change their pH as a function of temperature (which is discussed in more detail in the calibration section below). If the solution has solids in contact with it (as is the case with saturated limewater in the presence of excess solids), the temperature can also impact how much acid or base is in solution impacting pH, and how much is just solid sitting on the bottom of the container. These effects are specific for every solution that you will encounter, and there is nothing general that one can or should do about this, except be aware that it happens.

The second impact of temperature is on the pH electrode itself. pH electrodes change their response in a very clear way as temperature is changes. They respond more strongly to pH changes at higher temperature than at lower ones. At 100 ºC, they change their output potential by 74 mV/pH unit, and at 0 ºC, they change by 54 mv/pH unit. Because pH meters are typically standardized at pH 7 (that is, zero mv = pH 7), the error from temperature differences gets greater and greater as the pH being measured gets further from 7. So it may be trivial when measuring something with a pH of 7.1, but very important when measuring something with a pH of 10 (or when calibrating with a pH 10 buffer).

There are usually three different ways of taking temperature into account. One is to make measurements close to the temperature at which you calibrated the meter (say, within a few degrees). The second is to “tell’ the meter what the temperature is (digitally or with a dial). The third is that some meters have a temperature probe, usually called an ATC, which you stick into the measuring solution. This probe reports the temperature back to the meter, and the meter makes any necessary corrections (for this type of temperature effect).

As long as you use one of these three ways of dealing with temperature issues, you will get reasonably accurate readings.

From this thread:

https://www.reef2reef.com/threads/h...e-carbonate-equilibrium.1118837/post-13704874

Thanks. Very helpful.

I’ll make the temperatures of the samples at the time of pH measurement the same. Now to understand if the temp impact on the solubility of CO2 during the aeration step is a big enough impact to worry about. I found a couple papers about temp impact on seawater pH but they are behind the paywalls so I cannot see the data.

I just had an idea, which @Miami Reef is probably the only person who would care even a tiny bit.

I used the spreadsheet for making the iso-alkalinity graph to approximate the pH of the sample at 21C and 26C.

The sample aerated outside at 21C, then warmed up in a sealed container, will have a pH of 0.02 lower than if was aerated at 26C due to the difference in CO2 solubility. That’s more than I thought it would be!

 

[Miami Reef]

The sample aerated outside at 21C, then warmed up in a sealed container, will have a pH of 0.02

A +/- 0.02 pH difference between 9F is actually pretty low IMO.

 

[rishma]

The sample aerated outside at 21C, then warmed up in a sealed container, will have a pH of 0.02

A +/- 0.02 pH difference between 9F is actually pretty low IMO.

To be clear, it’s not the temp difference directly effecting the probe in my example. It’s the difference in CO2 solubility. I didn’t describe it well, but basically I changed the CO2 in the water to simulate aeration at a different temp rather than changing the temperature. That was supposed to approximate my warming the sample back up in a sealed container. I guess i expected the effect to be smaller than I could measure.

 

[Miami Reef]

To be clear, it’s not the temp difference directly effecting the probe in my example. It’s the difference in CO2 solubility. I didn’t describe it well, but basically I changed the CO2 in the water to simulate aeration at a different temp rather than changing the temperature. That was supposed to approximate my warming the sample back up in a sealed container. I guess it expected the effect to be smaller than I could measure.

Ah I see. Thank you for clarifying.

 

[Randy Holmes-Farley Verified Community Expert]

The temp effect on pH measurement can be avoided by allowing the sample to warm up while closed to the air.

The effect of CO2 solubility is not easily corrected except mathematically using some sort of tables of solubility , but I also do not think it likely to be large unless the temp is very low.