Preventing algae in a koi pond involves managing sunlight, nutrients, and water circulation. Algae thrive when the pond receives too much direct sunlight and when nutrient levels, especially nitrates and phosphates from fish waste or decomposing plants, are high. One way to reduce algae growth is by providing shade using floating plants, water lilies, or strategically placed trees and shrubs.
These plants also compete with algae for nutrients, helping to keep the water balanced. Avoid overfeeding your koi, since uneaten food increases nutrient levels that promote algae blooms. Keeping the pond clean by removing debris and performing regular partial water changes helps reduce excess nutrients. A good filtration system and proper water circulation prevent stagnant areas where algae tend to grow. Some pond owners use ultraviolet (UV) clarifiers, which expose water to UV light to kill free-floating algae cells and keep the water clearer.
