Lowering pH with CO2

[Jakebear]

Here's one for the Chem Geek---

I read you can lower the pH using CO2 --- how much would it take to go down let's say --- .2 ?? (More than the bottle on the Beer Tap?? ) Using a 10000 gal pool for reference.

[chem geek]

The answer depends on your starting and ending pH and on your TA level, but for going from 7.5 to 7.3 with a TA of 100 (and CYA of 30 and no Borates), it would take introducing 3.1 moles (about 136 grams or 4.8 ounces weight; at standard temperature and pressure, this is about 76 liters or 20 gallons of CO2 gas) of carbon dioxide to be added to a 10,000 gallon pool, fully dissolving into it (i.e. not just bubbling right out again). By the way, just as outgassing of CO2 increases pH with no change in TA, adding CO2 to your pool lowers pH with no change in TA as well.

Why do you ask? What source of CO2 do you have?

Richard

[Jakebear]

My source is just HIS beer tap Also he has a MIG welder with a big CO2 bottle for the shielding gas.

Just a curiosity -- When I saw the mention in an article it made the wheels start to turn, but it seems that unless you had a cheap source of dry ice (I don't) it would never be economical. say nothing about cooling the pool, dry ice being -200+degrees or something like that (COLD)

The chemistry of all these different chemical reactions fascinates me (H+O2 = water). I'd love to see a rundown of all of them in the Geek section of China Shop, when Ben puts that together. I'm sure you would be the A#1 contributor.

Thanks for your EXPERTISE!!

[chem geek]

The chemistry of all these different chemical reactions fascinates me (H+O2 = water). I'd love to see a rundown of all of them in the Geek section of China Shop, when Ben puts that together.

You can get quite a good fill of equations by looking at the spreadsheet linked at the end of the Pool Water Chemistry post in the China Shop.

Richard

[mas985]

So does that mean it would take about 5 oz of dry ice?

That would be interesting to compare cost to acid. Storage would be an issue but if you can get it cheap enough, then losing a little might not matter.

[mas985]

Just found this:

http://dryicedelivered.safeshopper.com/4/cat4.htm?299


25 lbs for $40 delivered. So that is 80 doses for $.50 per dose. Muriatic is about 8 oz for a .2 PH change or 16 doses per gallon @ $8/gallon or $.50/dose.

Oh well.

[chem geek]

So does that mean it would take about 5 oz of dry ice?

Yes, you are correct. But as your later post showed, it isn't more economical than Muriatic Acid and storage would be a bear, requiring one of those special high-efficiency thermos-type containers. Kind of interesting how the prices worked out to be similar. Thanks for doing that research.

Oh yeah, as for lowering the pool temperature, this would be pretty negligible for the amount that would be added to the pool. Dry ice is no warmer than about -109F or -79C but even if it were colder than that, the amount would hardly budge the pool temperature. One gallon of some substance that was even at absolute zero (which is impossible and is about -460F or -273C) mixed with 10,000 gallons of pool water at 80F would only lower the temperature by 0.05F or less than a tenth of a degree (assuming similar heat capacities for water and the substance, but even with a typical difference, we're still not talking about a large shift in temperature).