String Algae & White Foam in Shaded Pond: Causes & Fixes

5x8x3 ft pond, waterfall, UV, 6 goldfish. Clear but not crystal. White foam at waterfall/edges. Green string algae on rocks since leaves fell (more sun). Pump runs well.

String Algae Cause

Leaves fell → more sunlight + fewer plants (shade lost) = algae bloom. UV doesn't kill attached string algae.

White Foam Cause

Excess dissolved organic carbon (DOC) from fish waste, decaying leaves, or source water phosphates. Foam = DOC + agitation.

Solutions

1. Scrub rocks to remove string algae manually.
2. Add floating plants (hyacinth, lettuce) for shade/nutrient uptake.
3. Run UV 24/7—helps free-floating algae.
4. Try unplugging UV briefly—some ponds need beneficial bacteria UV kills.
5. Water changes reduce DOC/foam.
6. Activated carbon in filter adsorbs organics.

Seasonal leaf loss changes light balance—add plants to compensate.