Using dry ice to lower ph

Grape Ape

LifeTime Supporter
Jul 12, 2009
Seattle, WA
I’ve found a nearly free, if erratic source for dry ice and remembered this post: which tells me that one pound would drop my ph from 7.5 to about 7.25 which I have confirmed.

I want to use dry ice in lieu of muriatic acid when I can, does anyone have any hints or tips? Can I just throw it on the plaster in the deep end or will the cold damage it over time? I’ve already done it three times with no noticeable damage, but hate expensive surpises.

I’m considering fastening to cheap colanders together to create a sort of giant “tea ball” to keep it off of the plaster and shrink the bubbles down to increase the absorption of the CO2…


Well-known member
Jan 25, 2010
I think that the effect would be only temporary as the co2 that turns to carbonic acid would eventually outgas over a few hours- just a guess though

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
bk406 said:
Plus I would think your TA would increase as well.
The TA remains unchanged. It is the exact opposite of carbon dioxide outgassing. When adding carbon dioxide to the pool, such as with dry ice, the pH drops with no change in TA.

If one is lowering the pH that has risen from carbon dioxide outgassing, then it is the perfect see-saw with no change in TA. In practice, there will be a rise in TA over time from using chlorinating liquid or bleach from the excess lye and that will need acid to get the TA lowered again. The perfectly balanced situation would use enough acid to compensate for the excess lye in bleach and enough dry ice to compensate for the outgassing of carbon dioxide. Of course, one could just lower the TA level and have less of a pH rise in the first place.

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