Troubleshooting
Greater Duckweed problems — and how to fix them
Greater Duckweed (Spirodela polyrhiza) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Oxygen depletion under dense mats
Very thick mats block light and oxygen exchange at the water surface, reducing dissolved oxygen and stressing fish. Keep surface coverage to around 50% by skimming excess weekly during the growing season.
Rapid invasive spread
Spirodela can double biomass every 2–4 days in warm, nutrient-rich water. Control via regular skimming, shading part of the pond with marginal plants, or adding goldfish and koi that graze the fronds.
Wind concentration
Wind pushes floating fronds to one side of the pond, leaving the other side bare and concentrating plant material. This is natural but can worsen oxygen stress in the packed area; use a simple windbreak or add more marginal planting.
Prevent greater duckweed problems before they start
Most greater duckweed issues are care-mismatch, not bad luck. Dial in the basics:
Greater Duckweed problems — FAQ
Why is my greater duckweed oxygen depletion under dense mats?
Very thick mats block light and oxygen exchange at the water surface, reducing dissolved oxygen and stressing fish. Keep surface coverage to around 50% by skimming excess weekly during the growing season.
Why is my greater duckweed rapid invasive spread?
Spirodela can double biomass every 2–4 days in warm, nutrient-rich water. Control via regular skimming, shading part of the pond with marginal plants, or adding goldfish and koi that graze the fronds.
Why is my greater duckweed wind concentration?
Wind pushes floating fronds to one side of the pond, leaving the other side bare and concentrating plant material. This is natural but can worsen oxygen stress in the packed area; use a simple windbreak or add more marginal planting.