Aquatics Blog

pH Buffering

The world of pH buffering is changing. For years, pool operators had to choose between using CO2 or muriatic acid to adjust the pH of their pool. As time went on, some sophisticated operators installed both systems on their pools and manually switched between them to maintain the desired level of total alkalinity in the pool. And that was where the industry remained for many years, until now.

We live in a world where chemical controllers can function as building automation systems for the pool. This functionality has helped cause a major evolution in the world of pH buffering. Owners can now install a dual system of CO2 and muriatic acid that allows the controller to demand either chemical on a “time-based proportional feed system.” This simply means that the owner can control (through the chemical controller) how much CO2 is fed in proportion to acid. This is currently the only way to automatically control total alkalinity, as there are no chemical probes or other ways to digitally monitor it readily available. But, this technology allows for a pool’s total alkalinity to be maintained nearly automatically.

What is Total Alkalinity?

Total alkalinity is the measure of all dissolved bicarbonate (HCO3-), carbonate (CO3-), and hydroxide (OH-) ions.  It acts as a pH “buffer” in pool water to prevent large changes in pH. Low total alkalinity allows for rapid pH change, which makes it more difficult to control pH levels. Ultimately, this can contribute to corrosion in the pool. On the flipside, high total alkalinity makes adjusting the pH difficult, resulting in cloudy water and scaling. It’s important to find that total alkalinity balance to ensure the longevity of your facility.

CO2, as a pH buffer, raises the total alkalinity, while muriatic acid lowers it. If the source water has high total alkalinity (over 70 ppm), muriatic acid is recommended over CO2. Total alkalinity levels should be tested in all source water, along with calcium hardness and pH.

Industry standards typically recommend a total alkalinity between 80 and 120 ppm depending on the type of sanitizer used in the pool water.

Muriatic Acid

Muriatic acid is a 31.5% solution of hydrochloric acid typically used as a pH-buffering chemical. It’s usually automatically injected into the pool recirculation system in small amounts. The acid reacts with the sanitizer, thus counteracting the pH, and raising the effects of the sanitizer. In the pool, it will lower pH and total alkalinity.

Carbon Dioxide (CO2)

CO2 is an alternative pH-balancing chemical that is effective with “soft” source water. CO2 is a liquid, but when vented, it becomes a gas. It can be injected into the pool via a sand stone or mazzi injector. CO2 tends be more user-friendly and safer to handle than muriatic acid.

Carbon Dioxide is a liquefied gas that is both colorless and odorless. There are many regulations and standards surrounding its storage, so it’s important to remain aware of these. Tanks must be properly secured and segregated from any areas of activity, and the stored space should be well ventilated.

Adjusting Total Alkalinity:

Increasing total alkalinity involves adding one of the following chemicals to the pool: sodium bicarbonate, CO2 or baking soda (dry). Decreasing total alkalinity involves adding either sodium bisulfate (dry acid) or muriatic acid (liquid). When lowering total alkalinity, it is common to “slug the acid.” This means adding acid (liquid acid or pre-dissolved dry acid) to the deep end of the pool in a concentrated area.

Do You Need Both Systems?

The short answer: yes. Monitoring and controlling total alkalinity is an important part of maintaining water clarity. It’s something that should be tracked daily, and constantly kept in check. The same goes for pH and sanitizer levels.

The issue that we see with pools that utilize a single system is pool operators having to constantly add sodium bicarbonate or acid manually. As pool operators will tell you, this is no fun task, especially since it allows for inaccuracies. Dual systems eliminate the need to manually add either chemical and ensure levels are accurate.

We have seen some operators create a sodium bicarbonate slurry and setup a chemical feed pump to add it to the pool. However, this is still a manual system controlled by the operator, as the operator decides when to turn the system on and off based on total alkalinity readings. Additionally, this is not seen as an industry standard.


The perceived cost for dual systems is relatively small on a year-round pool. Most year-round pools are built with a chemical controller that could easily have this capability. The relative cost add is typically negligible when understanding the cost owners face buying other chemicals to maintain total alkalinity throughout the life of the facility. The difference: a dual system is part of upfront capital cost, and manually adding chemicals is part of operational costs.

Not Quite Industry Standard

While this idea is starting to take shape, it is not something that has been developed as an industry standard. The first of these systems should be installed in the summer of 2017. After these first systems are installed, it will be critical to collect feedback to help determine the potential for the system to be standardized.

If your chemical controller was installed prior to this timeframe, it will take some manipulation for the controller to be able to have this capability. However, some brands and models just won’t be able to. Most chemical controllers are actually built for a specific project. So if you are looking to add this feature, communicate with your aquatic engineer or chemical controller manufacturer to determine the best way forward.


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