Eliminating Blanket Weed (String Algae): Nitrogen Control, Shade, and Treatments

Cause: Excess Nitrate

Blanket weed thrives on high nitrate. Test with a kit (pH, ammonia, nitrite, nitrate).

Control Strategies

• Shade: pergola, netting, or a large shrub to block midday sun.
• Monthly 25% water changes (age tap water 24 hrs to dechlorinate).
• Blanket weed treatment (e.g., Hozelock 3539)—safe for fish.
• Don't over-clean bottom mud; it hosts beneficial bacteria.

Monitoring

Test weekly in summer. Adjust feeding and stocking to reduce nutrient load.