Algaecide is a chemical compound formulated to control or kill algae and cyanobacteria (often mistakenly called blue-green algae). The direct answer to whether algaecide kills algae is yes, but effectiveness depends heavily on the type of algaecide used, the species of algae present, and the overall water chemistry. Algaecides are intended to either destroy the algal cell structure or inhibit its growth and reproduction, making it easier for the primary sanitizer, such as chlorine, to eliminate the organism. Algaecide is only one component of a successful water maintenance program.
How Algaecides Function and Their Types
Algaecides are categorized into two main groups based on their active ingredients.
Non-Metallic Compounds (Quats)
The first group, non-metallic compounds, are often derived from quaternary ammonium compounds, commonly known as quats. These work primarily as contact killers by disrupting the algae’s cell walls and membranes. The positively charged quat molecules are attracted to the negatively charged cell surface, causing the cell to rupture and die.
Polymeric quats, or polyquats, are an advanced form of these compounds that are non-foaming and have a larger molecular structure. They function similarly to regular quats but last longer in the water, making them suitable for routine, preventative maintenance applications. Because they attack the physical structure of the cell, quat-based algaecides are effective across a broad spectrum of common algae strains.
Metallic Compounds (Copper)
The second major category is metallic algaecides, with copper being the most common active ingredient. Copper ions work by penetrating the algae cell and interfering with internal processes like photosynthesis and enzyme activity. By inhibiting the algae’s ability to metabolize nutrients and produce energy, the copper ions effectively poison the organism.
Copper-based treatments are often the preferred choice for aggressive or resistant strains, such as black or mustard algae. Careful dosing is necessary due to copper’s potency, as overuse can lead to water discoloration or staining of surfaces from precipitated copper compounds. Chelated copper formulations are designed to keep the copper ions suspended in the water longer, allowing for a more controlled and sustained release.
The Importance of Cleanup After Treatment
Killing the algae is only the first step; the resulting dead organic matter must be removed from the water. When a significant algae bloom is killed, the water often turns a cloudy gray or white as the dead cells float in suspension. This massive amount of dead algae biomass creates a high sanitizer demand, meaning the primary sanitizer will be consumed rapidly as it attempts to break down the organic debris.
In enclosed systems, such as pools, the dead cells must be filtered out to restore water clarity. Running the circulation and filtration system continuously for 24 hours or more is necessary to process the large volume of fine particulate matter. The filter media must be cleaned or backwashed frequently to prevent clogging and maintain flow.
For very heavy blooms, chemical aids like clarifiers or flocculants become necessary to assist the filtration process. Clarifiers work by binding microscopic dead algae particles into larger clusters that the filter can more easily trap. Flocculants create heavy clumps that sink quickly to the bottom, requiring manual vacuuming to waste and bypassing the filter entirely to avoid overwhelming it. In larger aquatic environments, the decomposition of a major bloom can deplete oxygen levels, potentially creating anoxic conditions that threaten aquatic life.
Preventing Algae Recurrence Without Chemicals
The most effective long-term strategy for algae control shifts the focus from reactive killing to proactive environmental management. Algae require sunlight, water, and nutrients, primarily phosphates, to thrive. Prevention involves manipulating the water chemistry to eliminate these favorable conditions.
Maintaining proper water chemistry is the first line of defense, particularly ensuring the pH is within the ideal range of 7.2 to 7.6. If the pH rises above this level, the primary sanitizer’s active killing component, hypochlorous acid, becomes less potent, allowing algae to flourish even with adequate sanitizer levels. Consistent free sanitizer levels (typically between 1 and 3 parts per million) are necessary to destroy any new algae spores as they enter the water.
Controlling the nutrient source is another preventative measure. Phosphates enter the water from sources like fertilizers, decaying organic matter, and some tap water supplies. Phosphate removers, often containing lanthanum compounds, are used to bind these nutrients, rendering them inaccessible to the algae.
Adequate circulation and filtration are also paramount, as stagnant water creates “dead spots” where algae spores can settle and grow undisturbed. Running the pump and filter for a minimum of eight to twelve hours daily ensures that water chemicals are distributed evenly and that any suspended debris or spores are pulled into the filtration system for removal. Regular brushing of surfaces, especially corners and crevices, prevents the initial attachment of algae colonies.