Pocket Botanist
Check these first
- Test your water for nitrate and phosphate levels.
- Check if you recently added any chemicals or cleaners to the water.
- Examine the water surface for any oily film or debris.
Likely causes
Nutrient Deficiency
Most likelyHow to tell: The fronds turn pale or develop yellow to brown spots when essential minerals like nitrogen or phosphorus are missing. This often happens in tanks with very few fish or no added fertilizer.
What to do: Add a small amount of liquid aquatic plant fertilizer to the water. Follow the instructions on the bottle for a low dose, as duckweed absorbs nutrients quickly. Monitor the plant for a week to see if new growth looks healthier.
Water Contamination
PossibleHow to tell: Dark or necrotic spots appear suddenly after you add tap water or new decor to the tank. This is often a reaction to chlorine or heavy metals in the water.
What to do: Use a water conditioner to neutralize chlorine and heavy metals before adding water to your tank. Perform a partial water change of 20 to 30 percent to dilute any existing contaminants. Always let new water sit for a few minutes before pouring it in.
Find out what's wrong with your duckweed
The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.
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When to worry
Worry if the spots spread rapidly across the entire colony, as this can lead to the plants sinking and rotting. A few individual spotted fronds are normal as the colony cycles through old growth.
Stopping it coming back
Keep your water parameters stable by performing regular small water changes and using a quality water conditioner. Ensure the plants have enough light to process the nutrients in the water.
Keep your duckweed healthy from here
Save your plant in Pocket Botanist and you get care reminders timed for this plant, plus a care history that shows what worked. Identification and a health check are free.
Questions people ask
- Can I save duckweed with spotted leaves?
- Yes, if you fix the water quality, the plant will usually produce healthy new fronds quickly. You can scoop out the heavily damaged leaves to keep the water clean.
- Do spots mean my duckweed is dying?
- Not necessarily, but it is a sign that the plant is stressed. Address the nutrient or water quality issue promptly to prevent the colony from collapsing.
More problems with Duckweed
This article was generated with AI from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.