Carbon Dioxide

CO2 is an alternative pH balancing chemical that is effective with “soft” source water. CO2 is injected into water to release oxygen and carbonic acid. Carbon dioxide is stored in 150 lb or 500 lb tanks.  CO2 is classified as an inert cryogenic liquid that is stored under pressure.

Some new CO2 tanks do not require heaters, but all require outside fill boxes.  Locate the tank remotely up to about 200 feet from the CO2 injection point.  The tank cannot be farther than 40 ft. from the fill box.  Use, when available, one of the many lease/fill programs that can save the owner money.

If a heater is required to prevent its respective feed system from freezing, it should be 7.5 amps.  Typically, a single 120 VAC electrical outlet at each of the CO2 feed systems is required for this purpose.

CO2 is a liquid and when it’s vented it becomes a gas. CO2 is non-flammable regardless of material state.  It is injected into the pool via a sandstone or a Mazzei injector.  CO2 is more user friendly for operators than muriatic acid.

Carbon Dioxide is a liquefied gas which is colorless and odorless. CO2 must be stored in accordance with all current regulations and standards.  The tanks must be properly secured and segregated from any areas of activity.  The stored space should be well ventilated.

CO2 tanks should have gauges for accurate output pressure control.

No fire rating is required. Dedicated storage room is still recommended for CO2 despite inert nature.

There are health risks associated with CO2 when there is a containment failure.  CO2 replaces oxygen and there is a potential for suffocation. Where small containers are used for indoor storage of CO2, a gas detection and audible alarm system capable of detecting CO2 emissions is required. Confirm with local codes for mechanical air change requirements in CO2 storage room. ACH requirement for CO2 room may be higher than mechanical space due to asphyxiation risk that is easier to achieve in a separate storage room with dedicated exhaust.

CO2 Exposure Limits are as follows:

Agency Low-end CO2 Concentration (ppm)1 High-end CO2 Concentration (ppm)2
OSHA PEL 5,000 TWA 30,000 STEL
ACGIH TLV 5,000 TWA 30,000 STEL
NIOSH REL 5,000 TWA 30,000 STEL

1 Applies to CO concentration in the workplace considered safe for a 40-hour week.
2 Based on a 10-minute period for NIOSH and a 15-minute period for OSHA and ACGIH.
PEL = Permissible Exposure Limit
TLV = Threshold Limit Value
REL= Recommended Exposure Limit
TWA= Time Weighted Average
STEL= Short Term Exposure Limit

Because carbonic acid is a relatively weak acid, it is not uncommon for pool operators to have a few gallons of muriatic acid on hand to assist in providing pH balance when filling the pool or when in need of a quick pH adjustment.  On occasion, muriatic acid may also be needed to adjust total alkalinity.

Since CO2 raises the TA in the water, it is CH’s preference to use muriatic acid on all pools where the total alkalinity in the source water is above 70 ppm.

Sanitation feed systems should be sized for a minimum of 3.0 ppd (pounds per day) of available chlorine for every 10,000 gallons of water volume, or 3.0 ppd of available chlorine for every 25 to 30 GPM of filter flow.

Sodium hypochlorite is about 12% to 15% available chlorine.  At 12%, one gallon provides about 1.0 lb of available chlorine.

Calcium hypochlorite is about 65% to 70% available chlorine.  One pound provides about 0.65 lbs of available chlorine.

  • 3 to 4 lbs of CO2 = 1 lb of muriatic acid.
  • 1.0 to 1.5 scfh CO2 = 1.0 pdd.
  • 30 scfh = 83 ppd CO2.

Approximately 1 gallon of muriatic acid is required to balance 3 gallons (or 27 lbs) of sodium hypochlorite.

Approximately 1 gallon of muriatic acid is required to balance 4.5 lbs of calcium hypochlorite.

1 to 1.5 lbs of CO2 is required to balance 1.0 lb of sodium hypochlorite.

9 to 13.5 lbs of CO2 is required to balance 1.0 gallon of sodium hypochlorite.

0.17 to 0.25 lbs of CO2 is required to balance 1.0 lb of calcium hypochlorite.

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