By Cassandra Tribe | Updated March 24, 2022
Maintaining the correct pH level—whether in swimming pools, aquariums, agricultural soils, or the human body—requires regular testing and precise adjustments. pH is the numerical scale that reflects the balance of hydrogen ions, essentially measuring how acidic or alkaline a substance is. Understanding the variables that shift this balance empowers you to keep your environment stable and healthy.
When CO₂ dissolves in water, it reacts to form carbonic acid, lowering the pH. Sources of dissolved CO₂ include respiration of fish and plants, decomposition of organic matter, and bacterial activity. In aquaria, high biological load or inadequate ventilation can quickly raise CO₂ levels, making regular CO₂ monitoring essential.
Water that flows over rocks, soil, coral, or organic debris can leach minerals such as calcium, magnesium, and sulfides. These ions combine with dissolved CO₂ or other constituents to produce weak acids or alkaline compounds, subtly shifting the pH over time. The specific impact depends on the local geology and the composition of the organic material.
Both sodium hypochlorite (NaOCl) and calcium hypochlorite (Ca(OCl)₂) are common disinfectants used in pool and potable‑water treatment. They release hypochlorous acid, which can slightly lower pH. Routine testing of water chemistry helps maintain the optimal pH range (typically 7.2‑7.8 for swimming pools).
When chlorine gas (Cl₂) is inadvertently released into the air—such as from over‑addition of liquid bleach—it reacts with moisture to form hydrochloric acid, rapidly dropping the pH of nearby water. Proper dosing and ventilation are critical to prevent this sudden shift.
Dust, pollen, and fine industrial particles can dissolve in rainwater or irrigation runoff, introducing trace acids or bases. Although each particle contributes a minute amount, their cumulative effect can alter the pH of soil or freshwater bodies, especially in urban or agricultural settings.
Industrial emissions and vehicle exhaust emit nitrogen oxides (NOₓ) and sulfur dioxide (SO₂). When these gases contact atmospheric moisture, they form nitric and sulfuric acids, respectively. Acid rain is a well‑documented phenomenon that lowers the pH of lakes, streams, and soil, impacting ecosystems worldwide.
