The Importance Of CO2 In Your Swimming Pool Water

Carbon dioxide is a colourless and odourless gas vital to life on Earth. Although it only makes up about 0.03-0.06% of our atmosphere, it exists almost everywhere and is an essential part of the lives of all living organisms — plants breathe in carbon dioxide while humans and animals breathe out. Since it’s such a common gas, we often disregard its value. Aside from its key position in nature, it’s also plays an important role in our swimming pool water.

Due to its chemical reactivity, CO2 is important in keeping the chemical levels in our swimming pools balanced. The effects of CO2 is very straightforward — when there’s more CO2 in the water, pH levels lower, but when there’s less CO2 in the water, pH levels rise. If there’s no carbon dioxide at all in the water, the pH level will be around 8.4, but if carbon dioxide is completely saturated in the water, then pH will drop to level 5. Keep in mind that the most suitable pH levels should remain between 7.2-7.8.

When acid is added into our swimming pools, carbon dioxide forms, and affects the pH level of our swimming pool water. Since it’s in water, the majority of the CO2 takes the form of aqueous CO2 while a small percentage reacts with water to form carbonic acid — H2CO3, which helps to lower the pH slightly. However, because of the equilibrium relationship between the CO2 in water and the CO2 in air, the pH level will return to its original state. Another way to add CO2 into our swimming pools is by injecting pure CO2 or adding dry ice (frozen CO2). Since CO2 will eventually off-gas, causing pH levels to rebound, CO2 needs to be added continually with a pH controller to keep the pH at low levels. Both methods —adding acid and adding CO2— will only change the pH level and not affect the alkalinity level.

Only dissolved CO2 will help calcium be soluble in water to maintain the right alkalinity level, so it is essential to have the right amount of CO2 in the water. Too much or too little CO2 will tip off the chemical balance in the water, and damage pool plasters, pool surfaces, and other parts of our pools. To reduce the amount of CO2 in our swimming waters, aeration methods, such as turning on the jets, or other functions that create air bubbles, are quick fixers that increase the surface area of water to air and encourage more off-gassing.

Maintaining the right pH level and alkalinity level is essential for you to enjoy your swimming pool. Levels that are too high or too low will damage both your swimming pool and your own health. If you need more advice on how to best utilize CO2, feel free to book an appointment today with Seaway Pools & Hot Tubs. We have many years of experience in all things pools and our experts will always help you find the best solutions for your needs. Don’t hesitate to contact us at 905-294-8030, or on our toll free number 1-888-494-8030, or by email at

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