High pH irrigation water is a common issue, especially if you are using well water. Many areas of the United States have high water pH and high alkalinity, and it directly impacts nutrient availability for your crops and can hurt distribution uniformity with drip systems. Getting that water pH down tol 6.5 is optimal for efficient irrigation. Several methods exist for acidifying the water, such as sulfuric, hydrochloric, organic acids, and carbonic acid (using CO₂). With many options it is worth comparing how the acids work in the water, the soil, and the overall safety.
Let's start by reviewing the two main reasons why managing high pH irrigation water is important: nutrient availability and bicarbonates/scale buildup.
High pH directly limits nutrient availability. As the chart below shows, vital nutrients (especially micronutrients like iron, zinc, phosphorus, and potassium) become 'locked up' and unavailable to plant roots above pH 7.0, even if present in the soil. This causes deficiencies and can limit yield. Adjusting water pH to the optimal 6.0-7.0 pH range, generally to 6.5, keeps nutrients soluble, improves plant uptake, and fertilizer efficiency.
High pH water often carries high bicarbonates (HCO₃⁻), which cause scale (calcium/magnesium carbonate) to precipitate (build up) inside pipes and emitters. This leads to clogging, poor distribution uniformity (DU), wasted water/energy, and increased maintenance. It can also affect yield from under watering. Lowering water pH prevents scale by converting bicarbonates to a more soluble form, keeping systems clean and efficient. When water reaches a pH of 6.5, almost half of the bicarbonates have turned into carbonic acid. This is true for any acid, and is part of the reason that 6.5 pH is considered the optimal target for pH to keep lines clean.
Managing nutrient uptake and scaling is important for getting the most out of your water, fertilizer, and irrigation system. (We'll take a deep dive on these two topics in a future post.)
Several common methods are used to acidify irrigation water, Sulfuric Acid, Hydrochloric Acid, and Sulfur Burners. Let’s look at those more closely:
A long-used standard, known for its strength in reducing pH. It’s very strong, and hasn’t met a pH that it can’t acidify. Long term, Its use can add sulfate (SO₄²⁻) to the soil system. This may be beneficial if sulfur is needed, but could be undesirable if soil or water sulfate levels are already high. It is highly corrosive, risky to handle, and dangerous for any individual to be around the tanks. It should be used with extreme caution. Any contact with skin must be immediately be followed by washing the affected area with water to avoid permanent damage.
Chemically lowers pH and is used as a base in some water treatment products. These products mix HCl with glycolic acid, surfactants, and quaternary organic soaps to provide other benefits. Overtime, using any HCl-based product adds chloride (Cl⁻) to the soil. This is a risk to chloride-sensitive crops (many fruits, nuts, vines) and can contribute to salinity problems. Hydrochloric acid is corrosive and should be handled carefully. Some videos show bare handling of diluted HCl-based products, but any skin contact with HCl should still be followed by immediately washing your hands, and all fumes should be avoided. Marketing around some products claims there is “permanent dissolution with no re-precipitation” of bicarbonates. These claims should be met with skepticism and are not backed up by practical understandings of bicarbonate chemistry.
These systems burn elemental sulfur pellets, producing sulfur dioxide gas, which dissolves in water to form sulfurous acid. This method lowers pH and adds sulfur compounds. This is a common solution for organic growers and many golf courses. The sulfurous acid is injected into the pond, mainline, or into a holding tank and then dosed. While the acid isn’t usually stored like sulfuric acid in a tank, it carries the same corrosion risks, and has less fine control in practice. Either the sulfur burner is on, or it's off. There is irritating smoke emitted during the burning process, which, according to many records, is mostly water vapor. Even if that is true, anyone who has been next to a sulfur burner can attest that enough sulfur dioxide gas is emitted to irritate anyone in a close proximity.
Consult with the Safety Data Sheet when handling any chemicals.
These methods can all work to control water pH, they have acidifying effects, and have been used by many growers and golf course superintendents. They work, but each comes with additional baggage, often in the form of adding compounds to the soil or safety risks. That is why many have switched to carbonic acid.
A reliable and increasingly utilized approach for water pH control is carbonic acid. This is created by fully dissolving carbon dioxide (CO₂) gas into the irrigation water. This process is sometimes referred to as Dissolved CO₂ in Irrigation Water (DCIW), and is a completely natural process.
How it Works: The CO₂ dissolves in water to form a safe, weak acid, carbonic acid (CO₂ + H₂O ⇌ H₂CO₃), which then releases hydrogen ions (H₂CO₃ ⇌ H⁺ + HCO₃⁻) to lower the water pH, just like any other acid. “Safe acid” isn’t a scientific metric, but just means that you can handle it with no safety or corrosion risks — it’s the same thing as rainwater and exists in club soda. “Weak acid” refers to the strength of an acid, not the pH, which is how easily the acid dissociates (donates a proton, H+, to a base) in a solution (represented by the Ka value). More of a weak acid is needed to shift the pH than a strong acid. That isn’t a bad thing, it means a weak acid can have a more fine “control” of the pH than a strong acid.
Functionality: Carbonic acid’s function is comparable to the effect of the other acids used for water pH control. It can readily achieve the target pH range, 6.5, and neutralizes bicarbonates, preventing nutrient lock-up and scale formation. Precise control using an automated feedback loop driven by a pH probe is common and automatically adjusts to changes in water quality. Carbonic acid is already used by plants in the Carbonic Acid Nutrient Exchange Theory, where carbon dioxide is released by roots to create carbonic acid to exchange nutrients from the soil particle.
Unlike mineral acids (Sulfuric or Hydrochloric), carbonic acid is carbon-based. After adjusting the water pH in the irrigation water and soil solution, carbonic acid reverts back to CO₂ and H₂O – natural components of the soil environment. The CO₂ stimulates microbial activity and can increase TOC and soil respiration, driving regenerative soil health benefits. There are no residual sulfates or chlorides from carbonic acid. This is an advantage for growers carefully managing nutrient balances or concerned about salt accumulation.
Not all common pH control methods can be used in organic operations, but certified organic growers do have tools available:
Derived from citrus fruits, citric acid is permitted for organic operations. While effective, larger quantities are typically required compared to strong mineral acids, and it can get expensive, especially for large-scale irrigation. In the soil, citric acid acts as a microbial food source, being readily biodegraded primarily into carbon dioxide and water. A potential secondary benefit of citric acid is its ability to chelate (bind) micronutrients like iron and zinc. It grabs onto micronutrients, keeping them dissolved in soil water so plants can absorb them instead of letting them get locked up as solids. This effect is temporary because soil microbes “eat” the citric acid.
This method, as outlined above, is allowed by CCOF for water pH control, and has been approved by the National Organic Standards Board (NOSB) for inclusion on the USDA National List of Allowed Substances (pending final rulemaking). This provides organic growers with a modern, practical option for precise water pH control. Organic Strawberry growers on the Central Coast have found carbonic acid especially beneficial with the high-bicarbonate water, and using CO₂, which is usually a waste, to improve water and align it with more natural processes is connected to regenerative organic agriculture.
Included on the USDA National List, as described earlier.
Choosing your pH management strategy involves weighing these factors. While traditional methods are established, they often come with handling risks and adding unwanted salts. Citric acid is a good option for soil health, but is not economically viable in most cases. Carbonic acid can provide precise, safe, scalable, water pH control without these drawbacks, and with additional benefits for soil biology.
There are many sources of salts that can cause issues in the soil and crop, so any product that will add to the salt load of the soil over time should be approached with caution.
“Salts reduce the osmotic potential of water, increasing the energy that plants use to extract moisture from soil, and making them more susceptible to wilting. In addition to contributing to water stress, some constituents of salts such as sodium, chloride and boron, are toxic if they accumulate in the leaves and stem. High sodium levels can also reduce the rate that water infiltrates into soil."
- Michael Cahn, Irrigation and Water Resource Advisor, University of California Cooperative Extension
Evaluating Salinity in Irrigation Water
While the immediate goal for water treatment is pH control, all soils should be thought of as more than just chemistry. The plant, soil, water, and each input are connected and includes the life in the soil. The chosen method can interact differently with the broader system over time.
Each input has an effect, using carbonic acid adds CO₂ to the soil, and avoids adding extra sulfur (Even though it is highly leachable, if there are infiltration problems, it can build up and cause nutrient imbalance issues), and hydrochloric acid can add unwanted chlorides.
Strong acids provide an additional hyper-acidification risk, where too much of the acid can easily be dosed and a dangerous and low pH can occur. This causes equipment corrosion and the strong acidity can kill the life in the soil. Look no further than a pump station that has used sulfuric acid or a sulfur burner for a few years.
A carbon-based component like CO₂ aligns well with regenerative soil health principles focused on carbon cycling and minimizing disruptive inputs.
While all properly managed acidification helps plants take nutrients, added salts cause long-term soil issues and hyper-acidification is a risk to the biological process that does the heavy lifting in the soil.
“Soil biological processes are responsible for supplying approximately 75 percent of the plant-available nitrogen and 65 percent of the available phosphorus in the soil.
Like all organisms, those inhabiting soil need food and a favorable environment. Adequate organic matter content, ample aeration, moderate moisture, neutral pH and warm temperatures all favor increased microbial activity.”
University of Minnesota Extension, Soil Biology
The pH control method matters with soil health. At ECO2MIX we have measured changes to key soil health parameters, and are continuing to work with partners to document the effects of carbonic acid on soil health, turfgrass, and crop production.
Microbiome Diversity
Decrease with Sulfuric: ↓ 12.95%
Increase with Carbonic: ↑ 12.34%
CO2 Respiration
Decrease with Sulfuric: ↓ 16%
Increase with Carbonic: ↑ 69%
Soil Organic Matter (SOM)
Decrease with Sulfuric: ↓ 4%
Increase with Carbonic: ↑ 124%
Total Organic Carbon (ppm)
Sulfuric: 115.79 → 106.72 (↓ Decrease)
Carbonic: 112.61 → 264 (↑ Increase)
Lowering the pH of alkaline irrigation water is the foundation of nutrient delivery and crop health. Water pH may not be at the top of your mind, but without consistent control, all nutrition and irrigation equipment efficiency will be affected.
That’s why, no matter which acid you use, regular water and soil testing is non-negotiable. You need to know your starting water pH and your alkalinity (bicarbonate level). Alkalinity dictates how much acid is needed, it’s the buffer that needs to be overcome to begin acidifying the water. Use reliable pH probes that are kept wet and calibrated often. With your dosing equipment, a pH probe and controller driving the dosing (an automated feedback loop) is necessary for consistent results and efficient use of the acid.
Sulfuric and hydrochloric acids offer traditional solutions, each adding specific residual ions. Citric acid can provide another route. For both conventional and organic growers, carbonic acid is a reliable, carbon-based alternative that achieves precise water pH control without adding residual salts, and supports natural soil processes.
If you don’t want to worry about your pH, consider switching to an ECO2MIX carbonic acid system—a fully automated, turnkey solution designed for safe and reliable performance. Fill out the form below to request more details or a proposal.
Got questions about water pH, carbonic acid, or something we didn’t cover? Drop us a message through the same form—we’re here to help.
