Koi fish do eat algae, but their feeding preferences are closely related to the types of algae. Here are the specific details:
1. Types of Algae Koi Will Eat
Planktonic Algae
They prefer diatoms, golden algae, yellow-green algae, and chlorella (single-celled green algae), as these are easily digestible and rich in protein.
When chlorella multiplies, the water turns green. While it helps purify water and supplement oxygen, it's advisable to control its overgrowth by adjusting light or salinity.
Filamentous Algae
They only consume soft, floating varieties (such as spirogyra) and show no interest in hard, substrate-attached filamentous algae (like moss).
2. Dual Roles of Algae
Beneficial Aspects
Moss (benthic algae) stabilizes water quality, serves as a natural food source for koi, and its presence indicates good water quality.
Green algae (chlorella) enhances coloration and absorbs ammonia nitrogen; moderate green water promotes koi growth.
Risks
Excessive planktonic algae (e.g., dark green water) or black hair algae (filamentous black algae) must be cleared promptly, as they can disrupt the ecological balance.
3. Precautions
Control Feeding Amount: Algae should be used as supplementary food; over-reliance on them may lead to nutritional imbalances.
Water Quality Management: Algae growth is directly related to water quality. Regular water changes and avoiding leftover food accumulation are essential.