pH is a measure of how acidic or alkaline water is, ranging on a scale from 0 to 14. A pH of 7 is neutral, values below 7 are acidic, and values above 7 are alkaline.
Algae are a diverse group of simple photosynthetic organisms, predominantly found in aquatic environments, that produce oxygen and form the base of many food webs.
This article clarifies how pH influences algae, explaining that high pH does not directly cause algae. Instead, it’s often associated with conditions favoring its proliferation or can result from significant algal activity.
The Relationship Between pH and Algae Growth
High pH levels do not directly initiate algae growth. Instead, elevated pH often indicates environmental conditions conducive to algal proliferation, or it can be a consequence of rapid photosynthetic activity by algae or other aquatic plants.
For instance, vigorous photosynthesis consumes carbon dioxide (CO2) from the water, which can lead to an increase in pH. This occurs because CO2 dissolved in water forms carbonic acid, and its removal reduces the water’s acidity, thereby raising the pH.
The availability of dissolved CO2 is significantly impacted by pH. In aquatic systems, CO2 exists in various forms depending on the pH, including dissolved CO2, bicarbonate ions (HCO3-), and carbonate ions (CO32-).
At higher pH, less free CO2 is available as the equilibrium shifts towards bicarbonate and carbonate forms. While many desirable aquatic plants rely on free CO2, some algae species utilize bicarbonate as a carbon source when CO2 is scarce. This adaptation gives them an advantage in high pH environments, allowing continued growth where other photosynthetic organisms might be carbon-limited.
High pH can therefore be a symptom of an existing algae bloom rather than its cause. As algae photosynthesize, they consume CO2, leading to a rise in pH during daylight hours. This daily fluctuation can be substantial in productive aquatic systems.
Prolonged high pH can stress beneficial aquatic plants, reducing their ability to compete with algae for resources, indirectly favoring algal dominance.
Other Key Factors for Algae Proliferation
While pH plays an indirect role, other factors more directly drive algae proliferation. Excess nutrients, particularly phosphates and nitrates, are the foremost cause of algal blooms. These nutrients act as fertilizers, fueling rapid growth. Common sources include agricultural runoff, wastewater discharge, decaying organic matter, and overfeeding in contained aquatic systems.
Light exposure is another fundamental requirement for algae, as they are photosynthetic organisms. Abundant sunlight provides the energy needed to convert carbon dioxide and water into biomass. Extended periods of intense light can significantly accelerate growth rates.
Water temperature also influences algae growth. Warmer temperatures generally promote faster metabolic rates in algae, leading to increased growth. Many species thrive above 60°F (15°C), with optimal ranges often between 20°C and 35°C, making summer months particularly prone to algal blooms.
Strategies for Algae Management
Effective algae management focuses on addressing the underlying conditions that promote their growth rather than solely targeting pH.
Controlling nutrient availability is paramount. This involves reducing external nutrient inputs by minimizing runoff from fertilized areas, properly managing waste, and avoiding overfeeding in aquariums or ponds. Regular water changes and removal of decaying plant matter can also help lower nutrient concentrations.
Managing light exposure is another effective strategy. In outdoor settings, increasing shade or reducing direct sunlight can limit algal photosynthesis. For indoor aquatic systems, controlling the duration and intensity of artificial lighting is important, with typical light cycles ranging from 8 to 10 hours per day.
Maintaining overall water chemistry balance, beyond just pH, is also important. While direct pH adjustment might seem appealing, it is more effective to address the root causes of pH imbalance, such as nutrient excess or insufficient CO2 for other plants.
Promoting healthy aquatic plants is a natural, sustainable method for algae control. These plants compete directly with algae for nutrients and light, effectively starving out undesirable algal growth.