I've got a 10L nano tank on my desk - fully planted. 4 minnows and a shed load of snails. The duck weed seems to double in number over night.

Printed this slotted spoon so that I can extract the duck weed from the floating feeding rings that I leave in the tank so that light can get to the submerged plants.

Overall the spoon is about 160mm from end to end.

Fusion 360 file included.