Carbon Dioxide CO2

For safer pH control in pools and spas

CO2 pH Control

Carbon Dioxide CO2 is a natural non-corrosive gas that can be used as a substitute for other acids (such as Muriatic acid HCl) in chemical treatment of pools and spas.

CO2 is available in standard pressurized gas cylinders. When dissolved in water, it forms carbonic acid H2CO3, a weak acid which can be used to lower the pH of water. and neutralize liquid chlorine.


  • No handling of corrosive acid containers,
  • No corrosion of equipment and facilities from acid fumes,
  • No dangerous chemical reactions with chlorine,
  • Less danger of excessive low pH in water. Because carbonic acid is a weak acid, the lowest pH value that can be reached is 6.8, even under accidental runaway conditions,
  • Optional AUTOMATIC SWITCHOVER assures continued control of pH.


  • CO2 increases the alkalinity of water and is therefore not recommended for applications where high alkalinity is a problem. Total Alkalinity (TA) should be maintained between 80 and 125 ppm.
  • High alkalinity increases acid demand, makes it difficult to lower the pH and may result in the formation of bicarbonate scale,
  • High alkalinity may be reduced with muriatic acid HCl or dry acid.


  • VICTOR SR 311 PRESSURE REGULATOR, factory set at 80 psi outlet pressure, with FLOWMETER, 30-100 scfh.
  • Three position Isolation Point Valve (IPV) with bracket set-up
  • Lifeguard safety high pressure hose, CO2 Type 30, 800 mm length
  • ASCO SOLENOID VALVE, brass body, 750 psi rating, 1/4″, 230V, 500r 60Hz. For connection to pH output relay of the CHEMTROL® controller.
  • PVC check valve/ injector 1/4″
  • FEED TUBE,  4.5 metre (15 ft)

*Recommended for pools up to 2,250,000 liter (500,000 gallons).


AUTOMATIC CO2 SWITCHOVER SYSTEM, designed for 2 or more cylinders on the same feed line, one being kept on standby until the first one is empty. The switchover automatically switches to the second cylinder when the pressure gets low. Additionally, more than one cylinder can be manifolded on each side of the swicthover to further increase the CO2 supply.


The schematic shows the principle of installation with an Automatic Switchover System which is recommended to assure continuous pH control. Control of gas injection is done by connecting the 230V pH control output of the CHEMTROL® controller to the solenoid valve on the CO2 injection line. One or more CO2 gas cylinders can be manifolded together on each line, depending on the feed rate required to maintain proper pH. Select the proper pressure regulator as indicated below according to pool size.