Carbon Dioxide
Carbon dioxide (CO2) in pool water forms carbonic acid, which influences pH and contributes to the natural downward pH drift in some systems.
Definition
Carbon dioxide (CO2) in pool water forms carbonic acid, which influences pH and contributes to the natural downward pH drift in some systems.
Typical Values: Naturally present; off-gassing rate increases with temperature and agitation
In Plain Language
Dissolved CO2 acts as a weak acid in water. Pools with high aeration (waterfalls, fountains, spa jets) off-gas CO2 rapidly, which raises pH as the acidic CO2 leaves the water. Conversely, adding CO2 gas (through a CO2 injection system) is an alternative to muriatic acid for pH control in commercial pools — it is safer and provides precise pH management. The relationship between CO2, pH, and alkalinity is central to water balance chemistry.
Why It Matters
Understanding CO2 off-gassing explains why aerated pools and hot tubs consistently drift toward high pH.
Typical Values
Naturally present; off-gassing rate increases with temperature and agitation
Last reviewed: 2026-06-01