Pond Bubbles and Foam: DOC, Soap, or Gas?

Pond full of bubbles; lots of plants, 8 goldfish. Asks if from decaying plants and if fish are safe.

Foam = DOC (Dissolved Organic Carbon)

Aeration (waterfall/fountain) fractionates DOC → foam. Sources: fish slime (parasites/injury), spawning fluids, excess food, rotting plants, fish waste.

Other Bubble Types

• Soap (malicious or accidental).
• Toxic gases (H₂S, methane) from deep sludge—burp up in neglected ponds.
• Plant photosynthesis (tiny bubbles on leaves, daytime only).

Action

1. Remove rotting plants.
2. Partial water change.
3. Add activated carbon to filter.
4. Test water if foam persists.

DOC usually low risk; high levels reduce oxygen, stress fish.