Winter Algae Control: String and Hair Algae in Cold Water

A pond with a Koi Dome has persistent string and hair algae at 40°F. The owner asks about winter-safe algaecides.

Algaecides Are Not Recommended

Chemical algaecides stress cold-water ecosystems and are especially harmful below 50°F. Avoid them.

Natural Management

• Hair algae thrive in cool water; physical removal is safe.
• Add competitive plants like watercress or water celery in the waterfall area.
• Test nitrate, pH, hardness, ammonia, and nitrite. High nitrate fuels algae.
• Barley straw and beneficial bacteria help long-term.

Algae isn't all bad—it provides oxygen and habitat. Focus on balance, not eradication. See algae control strategies.