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Pond Turns Black Overnight: Filter Check and Water Change

13x6x2 ft pond, 11 fish, 3 filters, hyacinths, plants. Water turned black in 2 days; waterfall black. Using Eco-system Aquaclearer Extreme dry bacteria. Clouded slowly then opaque.

System Out of Balance

Check filters: clogged? undersized? sponges saturated? Flow restricted? Hyacinths help but filters must handle load.

Immediate Steps

Clean/inspect all filters thoroughly.
10% water change to freshen.
Verify pump flow.
Black color suggests anaerobic breakdown or massive algae die-off.

Don't fill in pond yet—fix filtration first.

Pond and Water Gardening: Yellow Leaves on Houseplants: Watering Problem (Usually Too Much); Winterizing a Koi Pond in North Carolina; Milky White Water in New Pond: Causes and Cures; Persistent Green Algae in Large Koi Pond: Filter Maturity and Maintenance; Fixing Cloudy Pond Water and Black-Coated Waterfall Rocks; Kidney Pond (3×1 ft) Green Algae Constantly; Chronic Cloudy Water in a Sun-Exposed Pond: Fine Particles from Roots and Fish; Cesspool-Smelling Large Pond: No Outlet = Stagnation Death; Water Hyacinth Yellowing: pH, Sun, or Fish Eating Roots; Clearing Tea-Colored Pond Water Caused by Tannins

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