Algae Control by Competition, Not Eradication
Why algae and duckweed take over ponds
If algae or duckweed are persistent in your pond or lagoon, the root cause is almost always excess bioavailable nitrogen and phosphorus combined with sunlight and long hydraulic retention time. When biological competition is weak, algae efficiently capture nutrients during peak light periods and convert them into biomass.
Killing algae without addressing nutrient availability only resets the cycle. As long as nutrients remain available, regrowth is inevitable.
What bioaugmentation actually does and does not do
Bioaugmentation does not kill algae. It does not poison cells or chemically destroy biomass.
Instead, it works by restricting nutrient availability.
Augmented heterotrophic bacteria rapidly assimilate orthophosphate and ammonia, converting dissolved nutrients into bacterial biomass that can be settled or otherwise removed. When nutrient uptake occurs during daylight hours, algae are left nutrient-limited and unable to sustain growth.
This mechanism is most effective when:
- Readily biodegradable carbon is present or supplemented
- Phosphorus is the limiting nutrient
- Retention time allows bacterial populations to establish
Phosphorus-accumulating organisms further enhance phosphorus removal through luxury uptake.
Shifting the microbial ecology
With sufficient bacteria and carbon, the system shifts from free algae toward floc-forming bacterial biomass. This shift:
- Increases turbidity and shading
- Reduces photosynthetic efficiency
- Strengthens competition for trace nutrients
Algae decline through ecological displacement, not direct destruction.
Enzymes and algal byproducts
Bioaugmentation also introduces an enzymatic component. Enzymes degrade algal extracellular organic matter, reducing slime layers, surface mats, and floating biomass that interfere with clarification.
Indirect DO and pH stabilization
As algal density decreases and bacterial respiration increases, diurnal DO and pH swings are dampened. Reduced daytime oxygen spikes and nighttime crashes create conditions that are less favorable for algae and more stable for nitrifiers.
Design and operational considerations
- Carbon availability may require low-level supplementation
- Dose early morning or dusk to avoid UV exposure
- Avoid hydraulic short-circuiting
- Expect 2–6 weeks for visible improvement
- Apply early, before blooms dominate
Bottom line
Bioaugmentation is a long-term algae suppression strategy that works by limiting nutrients and stabilizing system biology—not by killing algae.
