Planted Tank Enthusiast
Join Date: Apr 2007
Location: Pine Knoll Shores
Duckweed is evil, imo. Sure, it's a great nutrient suck and certain creatures may enjoy it, but it gets everywhere, reproduces too quickly, and is very difficult to remove completely. There are better low maintenance and low light floating plant options.
Manually remove as much as you can (as safely as possible), and mist the remnants daily (lightly) with peroxide. Keep doing this until last plantlet is gone. Replace with Frogbit, Salvinia, Dwarf Water lettuce, or maybe even greater duckweed.