Aeration - how much does it raise your PH ?

[Riddler0520]

Hi folks,

I know aeration increases PH - is there a method to gauge how much it increases and for example, estimate if you turn water features off for 1/2 the time what that will do ?

I have the sheer decent and 2 bubblers on 12 hours a day and the Spa spillover cuts on 2x to turn over the spa water.

Check out the clip below and you see see the features and aeration occurring

Thoughts ?
I am adding acid about every 2-3 days right now (maybe 3-4 cups) drops it to 7.6 range and within a few days it’s purple - the 8.2 range/higher

 

[mas985]

I am not aware of any methods for predicting PH rise. Why not just turn it off and see if it slows down? That will be the most accurate method of determining the effect.

I am adding acid about every 2-3 days right now (maybe 3-4 cups) drops it to 7.6 range and within a few days it’s purple - the 8.2 range/higher

Note that if you rely upon high PH/TA fill water that will also contribute to PH rise.

 

[JamesW]

The amount of pH rise depends on the amount of carbon dioxide, the water temperature and the amount of agitation.

Think of a beer or soda going flat; letting it get warm or shaking it will cause the carbon dioxide to come out.

The amount of carbon dioxide depends on the TA (Carbonate Alkalinity) and the pH.

H₂CO₃ <--> HCO₃^- + H⁺

Carbonic acid or carbon dioxide <--> bicarbonate + hydrogen ion.

Here are the percentages of carbonic acid (carbon dioxide) vs. bicarbonate based on pH.

As you can see, the amount of carbon dioxide is a lot higher as the pH is lower.

pH.......H2CO3.............. HCO3-

6.0........69%..................31%

6.2........59%..................41%

6.4.......47%...................53%

6.6.......36%..................64%

6.8.......26%.................74%

7.0.......18%.................82%

7.2.......12%................88%

7.4.........8%................92%

7.6.........5%.................95%

7.8.........3%.................97%

8.0.........2%................98%

If you reduce the amount of bicarbonate (TA) or if you keep the pH higher, the amount of carbon dioxide is reduced and the pH rise goes down.

The amount of carbon dioxide at a pH of 7.5 is twice as much as at a pH of 7.8, which means that the pH rise will be twice as much.

 

[NCMike]

I would turn off all water features unless you are outside enjoying them. I run all mine for about 5 minutes every morning on a schedule just to run fresh chlorinated water through the pipes. Other than that they only come on when kids are in the pool and request them. Mine drive up my PH really fast. When I was reducing my TA I could turn on all water features and send my PH above 8, then drop it down to 7.0 with acid and have it back up to 7.4 in a couple hours with all the water features running.

 

[JamesW]

Percentage carbon dioxide (Y-axis) vs. pH (X-axis).

 

[JamesW]

Percent bicarbonate (Y-axis) vs. pH (X-axis).

 

[JamesW]

The percentage is based on the total number of molecules.

So, at a pH of 6.35, half of the molecules are carbonic acid (carbon dioxide) and half are bicarbonate.

So, the total number of moles is double the number of moles of bicarbonate.

For example, if the pH is 6.35 and the TA is 100, then the number of moles per liter of carbon dioxide (carbonic acid) are equal to the number of moles per liter of bicarbonate.

So, for a pH of 6.35 and a TA of 100, the relative amount of carbon dioxide will be 100.

As you can see from the below chart, the amount of carbon dioxide is twice as much at a pH of 7.5 vs. a pH of 7.8, which means twice as much pH rise.

Ph.....Relative amount of carbon dioxide.

6.35..... 100
6.4.....89
6.5.....71
6.6.....56
6.7.....45
6.8.....35
6.9.....28
7.0.....22
7.1.....18
7.2.....14
7.3.....11
7.4.....8.9
7.5.....7.1
7.6.....5.6
7.7.....4.47
7.8.....3.55
7.9.....2.82
8.0.....2.24
8.1.....1.78
8.2.....1.41
8.3.....1.12

 

[Riddler0520]

The amount of pH rise depends on the amount of carbon dioxide, the water temperature and the amount of agitation.

Think of a beer or soda going flat; letting it get warm or shaking it will cause the carbon dioxide to come out.

The amount of carbon dioxide depends on the TA (Carbonate Alkalinity) and the pH.

H₂CO₃ <--> HCO₃^- + H⁺

Carbonic acid or carbon dioxide <--> bicarbonate + hydrogen ion.

Here are the percentages of carbonic acid (carbon dioxide) vs. bicarbonate based on pH.

As you can see, the amount of carbon dioxide is a lot higher as the pH is lower.

pH.......H2CO3.............. HCO3-

6.0........69%..................31%

6.2........59%..................41%

6.4.......47%...................53%

6.6.......36%..................64%

6.8.......26%.................74%

7.0.......18%.................82%

7.2.......12%................88%

7.4.........8%................92%

7.6.........5%.................95%

7.8.........3%.................97%

8.0.........2%................98%

If you reduce the amount of bicarbonate (TA) or if you keep the pH higher, the amount of carbon dioxide is reduced and the pH rise goes down.

The amount of carbon dioxide at a pH of 7.5 is twice as much as at a pH of 7.8, which means that the pH rise will be twice as much.

Excellent explanation - I’m a photography nerd so I understand the doubling effect at 7.5 vs 7.8 similar to how aperture works and the impacts on shutter speed and ISO.

Fascinating to learn more about the science behind it - appreciate it

 

[Riddler0520]

I would turn off all water features unless you are outside enjoying them. I run all mine for about 5 minutes every morning on a schedule just to run fresh chlorinated water through the pipes. Other than that they only come on when kids are in the pool and request them. Mine drive up my PH really fast. When I was reducing my TA I could turn on all water features and send my PH above 8, then drop it down to 7.0 with acid and have it back up to 7.4 in a couple hours with all the water features running.

Understand - I work from home and enjoy just sitting out back and listening to the running water during conf calls where I can - maybe when I’m back traveling again I’ll cut them back but for now - it’s my zen space if that makes sense

at least what I’m seeing and adding acid every 2-3 days is normal … I’ll live with that for now as I’m using just over a gallon of acid a week so not that much