Green pond water is usually caused by single-celled algae suspended in the water, commonly called green water algae. These microscopic algae multiply rapidly when excess nutrients and sunlight are present.
Green water is especially common in new ponds and during seasonal changes when the pond's biological balance is still developing.
Common causes
- Excess sunlight: Encourages rapid algae growth.
- Excess nutrients: Fish waste, uneaten food, and decaying organic debris feed algae.
- Insufficient filtration: Allows organic waste and nutrients to accumulate.
- Limited aquatic plants: Reduces shade and natural nutrient absorption.
- New ponds: Beneficial bacteria and biological filtration are not fully established.
- Landscape runoff: Fertilizers and other nutrients entering the pond encourage algae growth.
How to clear green pond water
- Maintain filtration: Check pump operation and remove accumulated debris from pond filters. Clean filters as needed without unnecessarily disturbing beneficial bacteria.
- Remove organic debris: Use an Aquascape Pond Net to remove leaves, decaying vegetation, and other organic debris.
- Avoid overfeeding: Feed fish only what they can consume within approximately five minutes. Remove uneaten food.
- Add aquatic plants: Water lilies and other pond plants provide shade and absorb excess nutrients.
- Add beneficial bacteria: Use Aquascape Beneficial Bacteria or Beneficial Bacteria Concentrate to help reduce organic waste and excess nutrients. For newly established ponds, consider Pond Starter Bacteria. Follow product label directions.
- Use UV clarification: An Aquascape UltraKlear UV Clarifier or UltraKlean Pond Filter with UV helps eliminate suspended green water algae. Select a model appropriate for the pond size and water flow.
Important: Green water may improve naturally as the pond's ecosystem becomes established. UV clarifiers target suspended green water algae but do not eliminate string algae attached to rocks, waterfalls, or other pond surfaces.
Maintaining proper filtration, minimizing excess nutrients, and establishing a balanced pond ecosystem help prevent recurring green water.